Condensed Matter Physics Surface Physics - Experimentalphysik IV ...

RUHR-UNIVERSITÄT BOCHUM 

Condensed Matter Physics 

Surface Physics 

Annual report 

Jahresbericht 

2011

Institut für Experimentalphysik/Festkörperphysik & Oberflächenphysik 

Ruhr-Universität Bochum 

44780 Bochum 

Germany 

Telefon: +49 234 32 23 650 

Telefax: +49 234 32 14 173 

Internet: http://www.ep4.ruhr-uni-bochum.de

Institute for Experimental Physics Annual Report 2011 

Contents 

Introduction 1 

I Scientific Contributions 5 

Surface Studies 5 

Study of the thickness dependent magnetic and structural properties of ultrathin layers 

of Fe3Si on GaAs(001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

The influence of the substrate termination on the structural and magnetic properties 

of CrSb / GaAs(001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

HR-EELS measurement on zinc oxide powder samples . . . . . . . . . . . . . . . . . 11 

Magnetic thin films and heterostructures 13 

Anomalous Hall effect of Cu2MnAl, Co2MnSi and Co2MnGe Heusler alloy thin films 15 

Interface-induced room-temperature multiferroicity in BaTiO3 . . . . . . . . . . . . . 17 

Polarized neutron reflectometry study of the magnetic proximity effect in YBa2Cu3O7−δ/ 

La2/3Ca1/3MnO3 superlattices . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Magnetic nanostructures and nanoparticles 21 

Magnetizing interactions between Co nanoparticles induced by Pt capping . . . . . . 23 

Coupling behavior in iron-oxide nanoparticle/Py thin film composite systems . . . . . 25 

Structural and magnetic properties of self-assembled iron oxide nanoparticle superlattices 

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 

An experimental approach to a 2-dimensional magnetic network close to the percolation 

transition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 

Epitaxial self-assembly of iron oxide nanoparticles . . . . . . . . . . . . . . . . . . . . 31 

Polarized neutron reflectivity of monolayers of iron oxide nanoparticles at Super ADAM 33 

Magnetization reversal in dipolarly coupled PdFe nanodot arrays . . . . . . . . . . . 35 

Nucleation process of magnetic domains in Co2MnGe-Heusler nanostripes . . . . . . . 37 

Probing periodic permalloy stripe patterns with polarized neutron reflectometry . . . 39 

Dynamic Processes 41 

Time and element resolved magnetisation dynamics of ferrimagnetic GdFe in transmission 

geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 

Time-resolved XRMS in F/N/F trilayers (part I) . . . . . . . . . . . . . . . . . . . . 45 

Time-resolved XRMS in F/N/F trilayers (part II) . . . . . . . . . . . . . . . . . . . . 47 

Ferromagnetic resonance in the Co/Cu/Py system . . . . . . . . . . . . . . . . . . . . 49 

AC field stimulated dynamics of magnetization in iron film . . . . . . . . . . . . . . . 51 

Domain kinetics in iron film under AC magnetic field . . . . . . . . . . . . . . . . . . 53 

Instrumentation 55 

Vector- and angle-resolved MOKE measurements on Fe/MgO(001) as preparatory 

studies for time-resolved femtosecond laser scanning Kerr microscopy . . . . . . 57 

Design and results of the new Nano-MOKE setup . . . . . . . . . . . . . . . . . . . . 59 

Lithography Chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 

SuperADAM: recent developments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 

Imaging with Low Temperature Magnetic Force Microscope . . . . . . . . . . . . . . 65 

-i-

Annual Report 2011 Institute for Experimental Physics 

II Publications and Conference Contributions 67 

Published in 2011 67 

Published and to be published in 2012 69 

Conference Contributions 69 

III Invited Lectures, Talks, and Course Teaching 75 

Invited talks 75 

Committee and review panel work 77 

Course teaching 79 

Guest Lectures 81 

IV Workshops and Conferences organized by the Institute of Experimental 

Physics/Solid State Physics 83 

Concluding Conference of the SFB 491: Magnetic Heterostructures, September 26-29, 

2011, Ruhr-University Bochum . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 

Weihnachtskolloquium im Haus Herbede . . . . . . . . . . . . . . . . . . . . . . . . . 85 

V Personnel & On the Road 87 

Members of the Institute 87 

Academic degrees 88 

Bachelor of Science . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 

Diploma/Master . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 

Ph.D. Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 

Guests at the Institute 89 

Excursions 90 

On the road - Visits and Experiments at external facilities by members of the 

Institute 91 

VI Press & Alumni News 93 

Alumni News 93 

-ii-

Institute for Experimental Physics Annual Report 2011 

Editors: 

Oleg Petracic 

Hartmut Zabel 

-iii-


-iv-

INTRODUCTION 

Introduction 

In 1992 we have started the tradition of assembling annual reports on the scientific activies 

of the past year, including the scientific outcome in form of publications, seminars, conference 

contributions, etc. and last but not least on the most important measure of scientific success, 

which are the academic degrees granted. For the Diploma/Master and PhD students writing a 

contribution for the annual report has always been a healthy exercise. First it is an excellent 

training opportunity for composing a scientific text. Second it induces a critical reflection on 

the past year’s own progress. And third it provides a basis for a more extended manuscript to 

be submitted. The present 2011 annual report is the 20th edition of our annual reports and 

the last one. 

This is not the place to reflect on the past 20 years since the first annual report came out or 

the past 22 years since the arrival of Hartmut Zabel as chair of the Institute for Experimental 

Physics/Condensed Matter Physics. However the 30/60 PhD/Master students that have finished 

during this time and 8/4 more to be finishing during 2012 speak for themselves. This 

was scientifically a stimulating and lively time which to miss in the future will be hard to cope 

with. We are extremely thankful to our Master and PhD students for their hard work, their 

open minded approach to scientific questions, and their innovative power. Fortunately science 

is still well funded in Germany and therefore we expect that there will be plenty opportunities 

for future generations to work on challenging and exciting problems in the local University 

laboratory as well as at large scale facilities. 

The past year was under the focus of the terminating SFB 491: ”Magnetic Heterostructures: 

Spin Structures and Spin Transport”. After 12 years of funding by the DFG the SFB came 

to a closing by the end of 2011. During a concluding conference in the Conference center of 

the Ruhr-University Bochum, September 27-29, 2011 the members of the SFB 491 together 

with a number of referees had an opportunity to reflect on past highlights and future scientific 

challenges in the area of nanomagnetism. The reception in the newly furbished Kubus of the 

Haus Weitmar, the opening sesssion with the Presidents of both participating Universities, the 

scientific program, the poster session, and finally the Banquet in the Haus Herbede are lasting 

memorable events. This is the proper opportunity to thank again all helpful hands and in 

particular the local organizers Hanna Hantusch, Sabine Grubba, Jürgen Lindner, and Oleg 

Petracic for a smooth running of the conference. 

Although the SFB 491 funding has ended, life will continue - maybe not so well - and some 

tasks still need completion. Aside from 8 PhD students who need to finish during 2012/2013, 

from a more technical point of view the VEKMAG chamber at BESSY for scattering and 

spectroscopic studies at high magnetic fields and low temperatures needs completion and further 

upgrades of the Super ADAM polarized neutron reflectometer at the Institut Laue-Langevin 

needs attention. 

As already mentioned, we - the group leaders - are very proud of our Bachelor, Master, and 

PhD students, who spent much of their time in our laboratories, who team up for carrying 

out experiments at large scale synchrotron and neutron facilities, who write papers, beam time 

applications and reports, who prepare posters for workshops and conferences, and who finally 

write their thesis for defense against their referees. And often they fulfill in addition time 

consuming teaching duties. Considering all these tasks we are particularly proud of our four 

Bachelor students (Alexander Schwinger, Lina Elbers, Christian Klump, Dietmar Rother), our 

four Master students (Mathias Stadlbauer, Miriam Lange, Yu Gao, Wera Fehl), and our four 

PhD students (Philipp Gutfreund, Alexandra Schumann (Brennscheidt), Stefan Buschhorn, 

Mohamed Obaida), who have finished their thesis during the last year. We wish all alumni a 

-1-

successful professional future. 

INTRODUCTION 

Last but not least, we would like to thank all members of the Institute for their daily professional 

engagement to the benefit of the Institute and its many tasks. Furthermore, we are thankful 

to the funding agencies DFG, BMBF, DAAD, the Landesministerium für Wissenschaft und 

Forschung, and the Ruhr-Universität Bochum for their continuing support, which is much 

appreciated. Finally we would like to thank in particular our administrative and technical staff 

for their support, high motivation, and their dedication to the overall goal of the Institute 

beyond union boundary conditions. The last 22 years were a tremendously enjoyable time and 

I hope that the successor chair will have a similar experience. 

Ulrich Köhler Oleg Petracic Kurt Westerholt Hartmut Zabel 

-2-

INTRODUCTION 

FestKör 

FestKör per per physik 

physik 

R U B 

Prof. Hartmut Zabel 

Chair 

Bahar Öztamur 

Secretary 

Elisabeth Bartling 

Technician 

Frank Brüssing 

PhD Student 

Katherine Gross 

PhD Student 

Sani Noor 

PhD Student 

David Greving 

Master Student 

EXPERIMENTALPHYSIK IV 

FESTKÖRPERPHYSIK / OBERFLÄCHENPHYSIK 

Prof. Ulrich Köhler 

Group leader, Surface Physics 

Claudia Wulf 

Secretary 

Sabine Erdt-Böhm 

Technician 

Stefan Buschhorn 

PhD Student 

Sebastian Frey 

PhD Student 

Mohamed Obaida 

PhD Student 

Timo Lichtenstein 


Dr. Radu Abrudan 

Instrument Scientist 

Prof. Kurt Westerholt 

Group leader, Transport 

Dr. Giovanni Badini 

Post-Doc 

Cornelia Leschke 

Technician 

Astrid Ebbing 

PhD Student 

Martin Kroll 

PhD Student 

Philipp Szary 

PhD Student 

Derya Demirbas 

Diploma Student 

Anton Devishvili 

Instrument Scientist 

Condensed Matter Group (EP4), head Prof. H. Zabel 

Surface Science Group (AG4), head Prof. U. Köhler 

-3- 

PD Dr. Oleg Petracic 

Group leader,Nanostructures 

Dr. Ruslan Salikhov 

Post-Doc 

Jörg Meermann 

Technician 

Melanie Ewerlin 

PhD Student 

Min-Sang Lee 

PhD Student 

Caroline Fink 


Matthias Schlottke 

Diploma Student 

Kirill Zhernenkov 

PhD Student 

Prof. Boris Toperverg 

Group leader, Neutrons 

Dennis Schöpper 

SHK 

Jürgen Podschwadek 

Technician 


Carsten Godde 

PhD Student 

Chen Luo 

PhD Student 

Miriam Lange 


Lina Elbers 

Bachelor Student 

AG 

Oberflächen 

Hanna Hantusch 

SFB 491 Secretary 

Evgenij Termer 

SHK 

Peter Stauche 

Engineer 

Foto 

Dimitrii Gorkov 

PhD Student 

Durga Mishra 

PhD Student 

Deniz Özbek 


Christian Klump 

Bachelor Student

-4- 

INTRODUCTION

Part I 

Scientific Contributions 

Surface Studies 

-5- 

Surface studies

SCIENTIFIC CONTRIBUTIONS 

-6-

Surface studies 

Study of the thickness dependent magnetic and structural 

properties of ultrathin layers of Fe3Si on GaAs(001) 

S. Noor 1 , S. Özkan 1 , L. Elbers 1 , I. Barsukov 2 , N. Melnichak 2 , 

J. Lindner 2 , M. Farle 2 , and U. Köhler 1 

1 Institut für Experimentalphysik IV / AG Oberflächen, Ruhr-Universität Bochum 

2 Fachbereich Physik und Center for Nanointegration (CeNIDE), Universität Duisburg-Essen 

We consider the thickness dependencies of structure and magnetism of ultrathin 

layers of Fe3Si/GaAs(001). While the layer morphology exhibits a transition from 

cluster-wise growth at low coverage towards an almost layer-wise growth at higher 

coverage the magnetic behaviour changes from superparamagnetism to ferromagnetism. 

In addition to in situ STM and MOKE measurements a quantitative 

magnetic analysis was performed ex situ by SQUID and FMR. 

Among the ferromagnet/semiconductor systems 

which play a vital role for spintronic 

devices Fe3Si/GaAs is an interesting combination 

due to its small lattice mismatch, the halfmetallic 

behaviour of Fe3Si and the relatively 

small impedance mismatch compared to ferromagnetic 

metals. Also, as a binary Heusler 

alloy the growth of Fe3Si is easy to control due 

to its wide range in the phase diagram of iron 

silicides. 

In this contribution we investigate the 

structural and magnetic properties of 

Fe3Si/GaAs(001) for layer thicknesses ranging 

from 2 ML to 60 ML. Apart from the the 

thicknesses all samples were fabricated using 

the same conditions i.e. a growth rate of 0.1 

nm/min, a growth temperature of 200 ◦ C and 

post annealing at 300 ◦ C. All of the samples 

have a Si content of (23 ± 2) at.% as measured 

by RBS. 

Fig. 1: Left: Overview scan of 12 ML 

Fe3Si/GaAs(001) and the corresponding LEED pattern 

(107 eV). Right: Zooming in reveals the atomic structure 

which is face-centered with respect to the < 100 > 

directions. 

-7- 

Figure 1 shows STM scans of the surface morphology 

and the atomic structure alongside 

the corresponding LEED pattern for 12 ML of 

Fe3Si. At this thickness we already find an almost 

layer-wise growth with strongly oriented 

terrace edges along the [110] and the [1¯10] directions. 

On the atomic scale we find that only 

one sublattice of the D03 structure of Fe3Si is 

visible by STM. 

Fig. 2: Polar plots of normalized remanences as measured 

by LMOKE in the case of 12 ML (left) and 60 

ML (right). 

The polar plot of the magnetic remanences for 

the 12 ML sample as well as for a 60 ML sample 

can be seen in figure 2. A transition from a 

purely uniaxial anisotropy to an almost exclusively 

magnetocrystalline fourfold anisotropy 

can be observed. 

The surface morphology at low coverage is illustrated 

in figure 3. We find clusters with dendritic 

shapes whose edges are again oriented 

along the [110] and the [1¯10] directions and 

which already show some coalescence. The arrangement 

and lattice constants correspond to 

the D03 structure of Fe3Si. It was not possible


to obtain a ferromagnetic signal at this thickness 

for in situ MOKE which was later confirmed 

by SQUID measurements which show 

only very little or no splitting in the magnetization 

loop (left side of figure 4). This together 

with the island-like morphology points to a 

superparamagnetic behaviour. Indeed, this 

hypothesis was proven true by measuring zerofield 

cooling and field cooling curves where we 

found a splitting of these curves and a blocking 

temperature of 55 K (right-hand side of figure 

4). From measurements at a thickness of 5 

ML we can conclude that the transition from 

ferromagnetism to superparamagnetism must 

take place between 2 ML and 5 ML. 

Fig. 3: Overview scan of 2 ML Fe3Si/GaAs(001) and 

the corresponding LEED pattern (135 eV). 

Fig. 4: Left: Magnetization loop of 2 ML 

Fe3Si/GaAs(001) as measured by SQUID magnetometry 

at 300 K. Right: ZFC-FC-curve of the same sample 

(H = 20 Oe, ∆T / ∆t = 2 K / min). 

We fabricated a series of samples in order to 

determine thickness dependencies of the magnetic 

moment per atom and of the magnetic 

anisotropies. The magnetic moments are plotted 

in figure 5. Above a thickness of 20 ML 

the magnetic moment assumes values around 

the bulk value of 1.2075 µB. In contrast to an 

-8- 

expected reduced moment at lower thicknesses 

due to a diffuse interface we actually find an increase 

which might be attributed to increased 

orbital moments at the interfaces. 

Fig. 5: Magnetic moment per atom as a function of 

the Fe3Si layer thickness. The dashed blue line indicates 

the value of bulk Fe3Si. The insets show corresponding 

STM overview scans for 5 ML and 10 ML. 

The magnetocrystalline and the uniaxial 

anisotropy constants K4 and K2 measured by 

FMR are plotted in figure 6. K4 increases 

with increasing film thickness showing a large 

change in the range of 5 to 10 ML and satu- 

ration above. K2 shows an almost linear de- 

pendence versus 1/d according to K2 = K vol 

2 + 

K int 

2 /d favouring the [1¯10] direction. 

Fig. 6: Thickness dependencies of the in plane 

anisotropy parameters. 

We thank D. Rogalla and H.-W. Becker at the 

RUBION for performing the RBS analysis. 

Financial support through the Sonderforschungsbereich 

491 is gratefully acknowledged.


The influence of the substrate termination on the structural and 

magnetic properties of CrSb / GaAs(001) 

C. Godde, U. Köhler 

Institut für Experimentalphysik IV, Ruhr-Universität Bochum, Germany 

Investigations of half-metallic ferromagnets 

have been attracting considerable attention 

for spintronic devices, because these materials 

may provide 100 % spin polarization. Recently 

a different class of half-metallic ferromagnets, 

metastable zinc-blende CrAs and zinc-blende 

CrSb, have been grown epitaxially on III-V 

semiconductors by low-temperature molecularbeam 

epitaxy (MBE) [1]. Only ultrathin layers 

of CrSb or CrAs may keep their zinc-blende 

structure, and they relax into other stable nonzinc-blende 

phases at higher layer thickness. 

Thin CrSb layers grow in the zinc blende structure 

up to a thickness of 4nm on GaAs(001) 

[2] and keep their ferromagnetic properties 

and structural stability up to very high annealing 

temperatures which is interesting for 

enabling better crystalline quality. We investigate 

the growth of CrSb on the GaAs(001) 

surfaces at different coverages and annealing 

temperatures by STM and SQUID magnetometry. 

Particularly with regard to the existence 

of different phases at the GaAs(001) surface, 

we investigate the influence of a Ga- and an 

As-terminated surface of the substrate for the 

film deposition. The substrates for the experiment 

with the Ga-terminated surface were 

processed by cycles of sputtering and annealing 

to obtain a clean ordered surface. The 

As-terminated surfaces were processed in a 

Semiconductor MBE system by depositing a 

200nm GaAs layer on a commercial GaAs(001) 

wafer which is afterwards capped by an As 

layer (SFB 491, Project B10, A. Ludwig). After 

the transfer to the STM UHV system the 

As capping is removed by heating. The CrSb 

films are co-deposited on the GaAs substrate 

by MBE at a deposition temperature of 250 ◦ C 

with a co-deposition ratio of Cr and Sb: 1:6. 

On the GaAs(001) surface STM reveals for 

both substrate terminations a Volmer-Weber 

growth mode of the CrSb layers and atomic 

resolution show an ordering alongside the lattice 

structure of the substrate (see Fig.1 and 

Fig.2). For 3 ML CrSb STM does not show a 

closed film as proposed in the literature. There 

are islands with polycrystalline characteristics. 

Between these islands the substrate is visible. 

Although the deposited thin CrSb film on the 

Ga- and As-terminated surface show the same 

polycrystalline structural characteristics, the 

magnetic measurements offers very different results. 

The magnetic properties of co-deposited 

CrSb layers with a thickness of 3nm characterized 

by SQUID magnetometery are shown in 

the insets of Fig.1 and Fig.2. The hysteresis 

loops at roomtemperature show that indeed 

ferromagnetism exists in the CrSb layer grown 

on different terminated GaAs(001) substrates. 

For the As-terminated substrate (fig. 2) a ferromagnetic 

characteristics of the thin CrSb 

layers with a finite remanence and a magnetic 

moment per Cr-atom of up to ≈ 5 µB is measured 

which corresponds to the values found 

in the literature of CrSb-layers on GaAs(001) 

for burried CrSb layers [3]. In contrast, the 

CrSb islands on the Ga-terminated substrate 

(fig. 1) only offers a magnetic moment per Cratom 

of ≈ 1,5 µB, which is much smaller than 

expected [3] and a negligible remanence. Comparison 

of the CrSb layer on the differently 

terminated GaAs-substrates shows that the 

difference in the magnetic properties can not 

simply be expained by the island morphology 

or crystallographic arrangement and interface 

effects seem to play an important role. 

Acknowledgement: Financial support through the SFB 491 is gratefully appreciated. 

-9-


Fig. 7: 

CrSb layer of 3ML thickness co-deposited on the Ga-terminated GaAs(001) surface at 250 ◦ C. On the left is 

the corresponding magnetic hysteresis loop measured by SQUID at RT. Magnetic moment per Cr-atom of up 

to ≈ 1,5 µB 

Fig. 8: 

CrSb layer of 3ML thickness co-deposited on the As-terminated GaAs(001) surface at 250 ◦ C. On the left is 

the corresponding magnetic hysteresis loop measured by SQUID at RT. Magnetic moment per Cr-atom of up 

to ≈ 5 µB 

References 

[1] H. Akinaga, T. Manago, and M. Shirai, Jpn. J. Appl. Phys., Part 2 39, L1118 (2000) 

[2] J. J. Deng et al., J. Appl. Phys. 99, 093902 (2006) 

[3] J. H. Zhao, et al., Appl. Phys. Lett. 79,17 (2001) 

-10-

HR-EELS measurement on zinc oxide powder samples 

S. Frey, U. Köhler 



Advancement in preparing suitable samples for comparing in-situ measurements 

of single crystalline and powder zinc oxide with HR-EELS and STM are shown. 

Zinc oxide powders represent an important catalyst 

for a number of organic reactions, e. g. 

the synthesis of methanol. Corresponding surface 

science studies, on the other hand, mainly 

deal with single crystalline surfaces ([? ]). 

Since this situation is different from a real catalyst, 

it is reasonable to combine measurements 

of single crystals and powders to obtain supplementary 

results. 

The equipment of the UHV system (base pressure 


References 

[1] T. Löber, Diploma Thesis, Bochum (2006) 

[2] M. Kroll, U.Köhler, Surf. Sci. 601, 2182 (2007) 

[3] Y. Wang et. al., Phys. Rev. Lett. 95, 266104 (2005) 

Fig. 9: SEM images of a) a pressed and b) a sedimented zinc oxide film on a gold substrate. 

Fig. 10: HR-EELS signal of zinc oxide powder in comparsion to an adsorbate covered silicon single crystal. 

Fig. 11: HR-EELS signal of zinc oxide powder rotated by -3ˇr to 5ˇr (front to back) and 10ˇr (grey line) away 

from the central scattering position (red). 

-12-

Magnetic thin films and heterostructures 

-13- 

Magnetic heterostructures


-14-

Magnetic heterostructures 

Anomalous Hall effect of Cu2MnAl, Co2MnSi and Co2MnGe 

Heusler alloy thin films 

M. Obaida and K. Westerholt 

Institut für Experimentalphysik/ Festkörperphysik, Ruhr-Universität Bochum, Bochum, Germany 

We report on anomalous Hall effect (AHE) measurements of Cu2MnAl, Co2MnSi 

and Co2MnGe thin films Heusler alloys with different degrees of atomic order. 

The anomalous Hall effect (AHE) is a classical 

magneto-transport effect occurring in ferromagnetic 

metals in conventional Hall geometry 

along with the normal Hall effect. The 

total Hall electrical field of a ferromagnet can 

be written as 

E(H) = R0 · i · µ0H + RS · i · µ0M (1) 

with the magnetic field H, the current density 

i, the magnetization M, the normal Hall coefficient 

R0 and the anomalous Hall coefficient 

Rs. In the classical interpretation (see e.g. [1]) 

the anomalous Hall voltage is attributed to 

skew scattering at magnetic defects [2; 3] or to 

side jumps, a quantum mechanical mechanism 

where at every scattering process the electron 

is off-set perpendicular to the main current direction 

by a small distance [4]. Both effects 

originate from the LS-coupling of the conduction 

electrons, giving rise to an additional drift 

of the electrons perpendicular to the magnetization 

and the transport current. 

Examples of our results of the AHE measurements 

for the three Heusler phases in different 

annealing states are shown in Fig. 1(a-c) As 

common in the literature, instead of the Hall 

field E(H) we have plotted the transverse resistivity 

defined as ρxy = E(H)/i in Fig.1. 

In the as-prepared state and the other 

nanocrystalline states of Co2MnGe and 

Co2MnSi we find that AHE-coefficient is remarkably 

large, with the values for the Hall 

resistivity reaching up to ρxy=5 µΩcm and the 

corresponding anomalous Hall coefficient up to 

Rs=5·10 −8 m 3 /C as in Fig.2. The anomalous 

Hall effect for the samples in Fig. 1 dominates 

over the normal Hall effect even in the range 

of high fields, thus the normal Hall coefficient 

-15- 

R0 cannot be determined reliably. 

Fig. 12: Hall resistivity measured at T=2 K for 

Cu2MnAl (a), Co2MnGe (b) and Co2MnSi (c) annealed 

at different annealing temperatures Tann given 

in the figure. 

In the model of skew scattering the anomalous 

Hall coefficient should scale linearly with the 

longitudinal resistivity i.e. Rs ≺ ρxx, for the 

side jump mechanism and the intrinsic AHE 

Rs ≺ ρ 2 xx is expected [2; 4; 5]. For our samples 

Rs ≺ ρxx holds to a good approximation 

as shows in Fig. 3.


Fig. 13: The anomalous Hall constant Rs measured at 

2 K for Cu2MnAl (black squares), Co2MnGe (blue circles) 

and Co2MnSi (red triangles) versus the annealing 

temperature Tann. 

Fig. 14: The anomalous Hall coefficient versus the 

longitudinal resistivity, both measured at T = 2 K, for 

Cu2MnAl (a), Co2MnGe (b), and Co2MnSi (c). 

We encounter a quite peculiar situation in 

the AHE of the Cu2MnAl phase (Fig. 1(a)). 

References 

First, the magnitude of RS is about two orders 

of magnitude smaller than for Co2MnGe 

and Co2MnSi in the nanocrystalline state as 

well as in the crystalline state. Second, Rs exhibits 

a very different dependence on the annealing 

temperature with a maximum at intermediate 

Tann (Fig.2). Since the residual resistivity 

decreases monotonously with increasing 

Tann ,this implies that for Cu2MnAl there exists 

no scaling of the type ρxy ≺ ρ α xx 

Combining these results on the AHE for 

Cu2MnAl we suggest that the peculiar behavior 

results from a superposition of two components 

to the anomalous Hall voltage, one with 

positive and one with negative sign, nearly 

compensating each other. This would explain 

the small absolute value of Rs and the sensitivity 

to external parameters such as temperature 

and defect density. These two components 

can naturally be identified as the contributions 

from the spin-up and the spin-down electrons 

at the Fermi level. The LS-scattering mechanism 

scatters electrons with opposite spins into 

opposite directions and Cu2MnAl provides an 

example of an electronic energy band structure 

with very similar density of states for the spinup 

and spin-down electrons at the Fermi level. 

The calculated spin polarization at the Fermi 

level only amounts to about 20 % [6], thus 

both spin channels contribute nearly equally to 

the transport current. In this situation a compensation 

of their contributions to the anomalous 

Hall voltage seems feasible. This is in 

sharp contrast to the situation in Co2MnGe 

and Co2MnSi. where the polarization at the 

Fermi level is high or even complete and the 

transport properties are governed by the spinup 

electrons only . 

[1] C. M. Hurd,“The Hall Effect in Metals and Alloys” Plenum, New York. 1972 

[2] J. Smit, Physica, 21, 877. (1955) 

[3] J. Kondo, Prog. Theor. Phys., 27, 772.(1962) 

[4] L. Berger, Phys. Rev. B 2, 4559. (1970) 

[5] N. Nagaosa, J. Sinova, S. Onoda, A. H. MacDonald and N. P. Ong, Reviews Of Modern Phy., 82, 1539 

(2010) 

[6] J. Kübler, A. R. Williams and C. Sommers, Phys.Rev. B, 28, 1745 (1983) 

-16-


Interface-induced room-temperature multiferroicity in BaTiO3 

R. Abrudan 1 , S. Valencia 2 , A. Crassous 3 , L. Bocher 4 , V. Garcia 3 , X. Moya 5 , R. O. Cherifi 3 , 

C. Deranlot 3 , K. Bouzehouane 3 , S. Fusil 3,6 , A. Zobelli 4 , A. Gloter 4 , N. D. Mathur 5 , A. 

Gaupp 2 , F. Radu 2 , A. Barthélémy 3 and M. Bibes 3 

1 Experimentalphysik IV,Ruhr-Universität Bochum, 44780 Bochum, Germany 

3 Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489 Berlin, Germany 

3 Unité Mixte de Physique CNRS/Thales, France 

4 Laboratoire de Physique des Solides, Université Paris-Sud, France 

5 Department of Materials Science, University of Cambridge, UK 

6 Université d ′ Evry-Val d ′ Essonne, France 

Ferromagnetic and ferroelectric materials have potential applications in multistate 

data storage if the ferroic orders switch independently, or in electric-field 

controlled spintronics if the magnetoelectric coupling is strong. Here, we use soft 

X-ray resonant magnetic scattering to reveal that, at the interface with Fe or 

Co, ultrathin films of the archetypal ferroelectric BaTiO3 simultaneously possess 

a magnetization and a polarization that are both spontaneous and hysteretic at 

room temperature. 

The quest for materials showing ferromagnetism 

and ferroelectricity at room temperature 

remains a major challenge, the solution of 

which could unlock technological advances in 

numerous fields. Multiferroics showing strong 

magnetoelectric coupling could lead to spinbased 

devices with ultralow power consumption 

and novel microwave components. Multiferroics 

could also find applications as multiplestate 

data storage elements or multifunctional 

photonic devices exploiting non-reciprocal optical 

effects. 

Figure 15 shows a schematics of the investigated 

multilayer 30nm La2/3Sr1/3MnO3 

(LSMO) /2nm BaTiO3 (BTO)/2nm Fe sample. 

Due to the proximity of the Fe ferromagnetic 

layer to the ferroelectric BTO a 

ferromagnetic-like character is induced in the 

latter at the Fe/BTO interface. This interfacial 

BTO layer exibits therefore simultaneously 

ferromagnetism and ferroelectricity at room 

temperature. It is therefore a multiferroic [1]. 

All three layers are characterized by their respective 

hysteretic response, i.e. the change of 

ferroelectric or ferromagnetic state in response 

to an external electric field (E) or magnetic 

field (H), respectively: the Fe-layer by a ferromagnetic 

hysteresis, the BTO layer by a ferroelectric 

hysteresis, and the response of the 

-17- 

multiferroic interlayer that reacts upon both, 

electric field and magnetic field. The red arrow 

in Fig. 15 indicates the direction of the incoming 

synchrotron beam, which can be chosen to 

be either right of left circularly polarized. Soft 

x-ray magnetic absorption and scattering measurements 

were performed by using the ALICE 

diffractometer [2]. The degree of circular polarization 

(XMCD and XRMS measurements) at 

the PM3 beam line of HZB-BESSY II was 92%. 

Fig. 15: Schematic view of the investigated sample 

Fe(Co)/BTO. X-ray direction and polarizations are 

also indicated. 

Absorption and reflection measurements for 

the BTO/Fe sample were done using two different 

Cu sample holders : a). Absorption was simultaneously 

measured by means of total electron 

yield (TEY) and Fluorescence yield (FY).


The radiation impinged the sample at an angle 

of 20 ◦ along the incoming beam propagation 

direction b). For reflection, the sample 

was placed at incidence angles of 10 ◦ and 15 ◦ 

with respect the incoming propagation direction. 

The Fe and Co L3,2 -edge XAS and X-ray 

Magnetic Circular Dichroism (XMCD) spectra 

corresponding to the top layers are shown in 

Fig. 16 (a, d). Apart from a small signature 

from the Ba M5,4 edge visible in the Co XAS 

data, the spectra are typical of bulk bcc Fe and 

hcp Co, respectively. We note, however, that 

from these data we cannot exclude the presence 

of an ultra-thin Fe or Co oxidized layers 

at the metal/BTO interface. 

Fig. 16: Element specific magnetic signals at Fe/BTO 

and Co/BTO interfaces. 

The magnetic signal is expected to arise mainly 

from the very first BTO atomic layer in contact 

with the transition metal, and its detection 

by means of XMCD is challenging. It is 

well known that, owing to interference effects, 

the reflection counterpart of XMCD exhibits 

a higher sensitivity to interface magnetization 

and therefore allows the detection of smallest 

magnetic moments not detectable by means of 

absorption techniques. In Fig. 16 (b, c) the 

top panels show the XRMS spectra obtained at 

the O K-edge and Ti L3,2-edge for the Fe/BTO 

sample and the bottom panels present the associated 

XRMS asymmetry. In the case of 

non-magnetic Ti or O atoms, the asymmetry 

has to be zero. However, the data show a finite 

dichroism for Ti and O, thus evidencing 

the presence of magnetism in BTO. Although 

the dichroic signals are weak, they clearly reverse 

upon changing the helicity of the light 

(see Fig. 16 (b, c), bottom panels), which confirms 

their magnetic origin. Figure 16 (e, f) 

-18- 

show XRMS and asymmetry spectra for the 

Co sample. 

Fig. 17: a,b, Evidence for room-temperature multiferroicity 

via magnetic element specific hysterezis 

loops c, piezoresponse hysterezis loop d, Atomically 

resolved HAADF image of the Fe/BTO interface of 

the Fe/BTO(50 nm)/LSMO(30 nm) //NGO(001) heterostructure. 

To unambiguously demonstrate the long range 

ferromagnetic-like character of BTO, we have 

measured the dependence of the XRMS signals 

at selected resonant energies as a function of 

the magnetic field. Figure 17 (a) (Fe/BTO 

sample) and Fig. 17 (b) (Co/BTO sample) 

show the results for Fe or Co, Ti and O as 

well as Mn. All signals show clear hysteresis 

loops as a function of magnetic field. For the 

BTO/Co sample, all signals have virtually identical 

coercive fields, which could be coincidental, 

or indicate magnetic coupling of the LSMO 

and Co across the BTO film. Interestingly, electric 

field dependent magnetic coupling across 

ferroelectric films has indeed been predicted recently. 

For the Fe/BTO sample, the Ti and O 

signals reverse at the same magnetic field as 

the Fe, whereas the Mn signal - and thus the 

magnetization of LSMO - reverses at a lower 

field. This indicates that the magnetic moments 

carried by the Ti and O ions are coupled 

to the Fe, as expected if the Ti and O moments 

are induced at the interface with the Fe layer 

in agreement with theory. BMBF Contract No. 

05K10PC2 is acknowledged. 

References 

[1] S. Valencia et al. Nature Materials 10 753-758 

(2011) 

[2] J. Grabis et al. Rev. Sci. Instr. 74, 4048 (2003).


Polarized neutron reflectometry study of the magnetic proximity 

effect in YBa2Cu3O7−δ/ La 2/3Ca 1/3MnO3 superlattices 

M. A. Uribe-Laverde 1 , D. K. Satapathy 1 , I. Marozau 1 , V. K. Malik 1 , S. Das 1 , C. Bernhard 1 

A. Devishvili 2 , A. B. Toperverg 2 , H. Zabel 2 , C. Marcelot 3 , J. Stahn 3 , A. Rühm 4 and T. Keller 4 . 

1 University of Fribourg, 1700 Fribourg, Switzerland 

2 Ruhr-Universität Bochum, 44780 Bochum, Germany 

3 Paul Scherrer Insitute, 5234 Villigen, Switzerland 

4 Max-Planck-Institut, 70569 Stuttgart, Germany 

Atomically engineered multilayers combining materials with antagonistic orders 

such as superconductivity and ferromagnetism are not only offer unique opportunities 

to realize novel quantum states but also are important from technology point of 

view. In particular, oxide based superconducting/ferromagnetic multilayers allow 

one to utilize the high superconducting transition temperature of cuprates and the 

versatile magnetic properties of the colossal-magnetoresistance manganites. Recent 

measurements on SuperADAM reveal an intricate interplay between superconducting 

and ferromagnetic orders suggesting a sizable proximity effect taking place in 

these superlattices. 

Reflectivity 

10 0 

10 −2 

10 −4 

10 −6 

10 −8 

a) 

1 st 

300K 

100K 

10K 

2 nd 

0.03 0.06 0.09 0.12 

q z (Å −1 ) 

Unpol 

|++> 

|--> 

3 rd 

4 th 

SLD (10 14 m −2 ) 

5 

4 

3 

2 

1 

0 

Magnetic at 10 K 

Magnetic at 100 K 

Nuclear 

YBCO 

LCMO 

b) 

LCMO 

YBCO 

0 2 4 6 8 10 

z (nm) 

Fig. 18: a)Polarized neutron reflectivity curves as a function of the momentum transfer for a 

YBCO/LCMO superlattice at T=300 K, T=100 K and T=10 K. The arrows indicate the position 

of the superlattice Bragg peaks. The solid lines are the results of the fits. b) Nuclear and magnetic 

scattering length density inside the LCMO layers as obtained from the fits. 

The interaction between the superconducting 

(SC) and ferromagnetic (FM) orders has been 

broadly studied and is still the subject of ongoing 

research. First theoretical predictions 

-19- 

and later experimental proofs of proximity effects 

have opened a new door for potential 

applications[1; 2; 3]. Nevertheless, most of 

this work has been focused on conventional


low temperature superconductors and little is 

known about the interaction between superconductivity 

and ferromagnetism in oxide-based 

materials. These oxide based superconducting 

YBa2Cu3O7−δ (YBCO) and ferromagnetic 

La2/3Ca1/3MnO3 (LCMO) multilayers have obvious 

advantages, like high-TC of cuprates or 

the versatile magnetic properties of manganites 

which can be tailored by weak perturbations 

such as an external magnetic field and(or) 

even by close proximity to SC layers. Polarized 

neutron reflectometry (PNR), which probes 

the magnetic depth profile and its evolution as 

a function of temperature enables us to observe 

such weak perturbations. 

The studied superlattices consist of 10 repetitions 

of the bilayer structure with a nominal 

layer thickness of 10 nm. Figure 1 a) shows 

the reflectivity curves measured at different 

temperatures above and below the superconducting 

and ferromagnetic transition temperatures, 

TSC = 88 K and TC = 201 K respectively. 

Sharp and intense superlattice Bragg 

peaks, product of the constructive interference 

between reflections coming from all the interfaces, 

can be observed evidencing the high sample 

quality. At room temperature (green symbols), 

only the nuclear interaction of the neutrons 

is relevant and the even order Bragg 

peaks are strongly suppressed as expected for 

a superlattice with equal layer thicknesses. 

For the curves measured below the Curie temperature 

(red and blue symbols) intense even 

order Bragg peaks are observed which are the 

fingerprint of a reduced symmetry of the magnetic 

depth profile with respect to the nuclear 

one [4]. Figure 1 b) shows the nuclear and 

magnetic profiles for various temperatures as 

obtained from fitting the data (solid lines in 

figure 1 a)). The ferromagnetic moment is 

strongly suppressed on the LCMO side of the 

interfaces. Although the magnetic nature of 

these depleted ferromagnetic regions is not yet 

clear, their very large magnetic roughness and 

the anomalous evolution of their thickness with 

temperature suggest an inhomogeneous or oscillatory 

magnetic state. 

3 rd Bragg Peak Asymmetry 

-20- 

0.5 

0.4 

0.3 

0.2 

0.1 

T SC 

Reflectivity (x10 -4 ) 

0.0 

0 20 40 60 80 100 120 140 160 

Temperature (K) 

2 

1 

0 

|++> 

|--> 

100K 

4K 

0.09 0.1 0.11 

qz ( -1 ) 

Fig. 19: Asymmetry of the 3 rd order Bragg peak, 

(I −− − I ++ )/(I −+ + I ++ ), as a function of temperature. 

Dataset combines measurements from Super- 

ADAM (ILL), N-REX+ (FRM2) and AMOR (PSI). 

Inset: Reflectivity in the vicinity of the third Bragg 

peak showing the large splitting between the different 

spin channels below TSC. 

Figure 2 shows the temperature dependence 

of the asymmetry of the 3rd order superlattice 

Bragg peak. This asymmetry remains 

very small above 90K and it exhibits a clear 

anomaly below TSC which reveals that the onset 

of superconductivity in the YBCO layers 

gives rise to marked changes of the depleted 

layers in LCMO. As shown in Figure 1 b), the 

thickness of the depleted layers gets reduced 

below TSC. 

The PNR measurements on SuperADAM reveal 

a fascinating magnetic proximity effect 

which unambiguously confirms the presence of 

a layer, at the LCMO side of the interface 

where the FM order of the Mn moments is 

strongly supressed. In addition, the superconductivity 

induced change in the thickness of 

the depleted FM layer, is indicative of a sizeable 

coupling between superconductivity and 

ferromagnetic orders across the interface. 

References 

[1] A. I Buzdin, Rev. Mod. Phys. 77 (2005) 

935. 

[2] F. S. Bergeret et. al. Rev. Mod. Phys. 77 

(2005) 1321. 

[3] M. Eschrig, Phys. Today 64 (2011) 43. 

[4] J. Stahn et. al. Phys. Rev. B 71 (2005) 

140509.

Magnetic nanostructures and nanoparticles 

-21- 

Lateral structures


-22-

Lateral structures 

Magnetizing interactions between Co nanoparticles induced by Pt 

capping 

A. Ebbing 1 , L. Agudo 2 , G. Eggeler 2 and O. Petracic 1 

1 Institut für Experimentalphysik/Festkörperphysik, Ruhr-Universität Bochum, Germany 

2 Institute for Material Science, Ruhr-Universität Bochum, Germany 

By capping self-assembled Co nanoparticles (NPs) with Pt the magnetic properties 

can be strongly influenced. With an inceasing amount of Pt deposited onto the 

NPs a strong magnetizing interaction between the NPs can be induced. 

The samples were prepared at room temperature 

using Ar ion beam sputtering at base pressures 

better than 5 × 10 −9 mbar using highly 

purified Ar gas. After sputtering the amorphous 

Al2O3 buffer layer of 3.4 nm thickness 

from an Al2O3 target onto Si substrates with 

a rate of 0.017 nm/s, a Cobalt-layer of nominal 

thickness tCo = 0.66 nm was sputtered 

from a Cobalt target at a rate of 0.03 nm/s. 

Due to extreme Volmer-Weber growth the Co 

forms isolated and nearly spherical particles [1]. 

These particles were then capped by sputtering 

a Pt layer with various nominal thicknesses 0 

≤ tP t ≤ 1.57 nm under a constant oblique deposition 

angle of 30 ◦ with respect to the surface 

normal. Finally, another alumina layer with a 

thickness of 3.4 nm was sputtered under constant 

rotation of the substrate to embed and 

to protect the NPs from oxidation. 

Fig. 20: STEM images of Co NPs without Pt capping 

(A), with tP t > 0.53 nm (B) and with tP t > 1.40 nm. 

Fig. 20 shows scanning transmission electron 

mircroscopy (STEM) images of samples with 

different amounts of Pt deposited onto the Co 

NPs. While the uncapped NPs are clearly 

sepereated with a mean diameter of 2.7 nm at 

average distances of 4.2 nm, for tP t = 0.53 nm 

the NPs are partially connected via bridges of 

Pt. For tP t = 1.40 nm the NPs are completely 

covered with Pt. 

-23- 

The magnetic properties have been studied using 

a superconducting quantum interference device 

(SQUID) magnetometer. 

Fig. 21: ZFC/FC measurements for different amounts 

of Pt. The measurements are performed in a small field 

of 20 Oe. 

Fig. 21 shows the ZFC/FC measurements for 

tP t =0.53, 0.70, 0.88 and 1.40 nm. For the Co 

NPs capped with Pt up to 0.53 nm the measurements 

reveal a superparamagnetic behavior 

which is independent of the sample history. 

The samples capped with tP t > 0.53 nm show 

different behaviour depending on the fields applied 

before cooling the sample in zero field. 

Therefore these ZFC/FC measurements are 

performed both after applying + 1kOe and -1 

kOe at 350 K. After the field was removed the 

samples were kept at 350 K for 30 min to allow 

for thermal relaxation. For the sample with tP t 

= 0.70 nm (Fig. 21b) both ZFC curves show a 

peak around 110 K, which fits well the blocking 

temperature of the sample capped with 0.53


nm Pt. In the ZFC curve obtained after a negative 

field applied at 350 K additionally a steep 

increase appears between 200 K and 220 K. 

A further increase in Pt capping results in a 

less pronounced peak at 110 K and a strongly 

enlarged increase around 210 K. Increasing 

the amount of Pt further leads to a complete 

switching of the magnetization around 210 K. 

The ZFC/FC measurements are comparable 

within a range of 1.05 nm ≤ tP t ≤ 1.57 nm Pt. 

The FC curves show the shape of a ferromagnetic 

order parameter and can be described using 

the semiempirical fit formula 

Ms(T ) 

Ms(0) = 

� � �p � � � 

5/2 

β 

T 

T 

1 − s − (1 − s) 

TC 

TC 

(2) 

where 0 3/2 are semiempirical 

fit parameters and β is the critical exponent 

of the order parameter [2]. 

This FM-like behaviour can be due to either 

single NPs acting as stable FM nanomagnets 

or a parallel coupling of the NP-superspins. A 

capable method to investigate the nature and 

strength of the coupling are δM curves following 

the expression 

δM(H) = 2MIRM(H) − 1 + MDCD(−H) (3) 

References 

[1] O. Petracic, Superlatt. Microstruct. 47, 569 (2010) 

[2] M. D. Kuzmin et al., Phys. Rev. Lett. 94, 107204 (2005) 

[3] P. E. Kelly, K.O. Grady, et al., IEEE Trans. Magn. 25, 3881 (1989) 

-24- 

[3]. For the IRM data the samples are demagnetized 

while for the DCD data the samples are 

fully negative magnetized. The following measurement 

procedure is the same for both cases. 

At a temperature of 5 K the field is succesively 

increased and the magnetization is measured 

between two field steps at 0 Oe. 

Fig. 22: δ M curves for different thicknesses of Pt. 

The δ M curves in Fig. 22 include a negative 

area which represents a demagnetizing interaction 

between the NPs that can be attributed to 

dipolar interactions. An increase in Pt results 

in a transition to a positive area included and 

therefore indicates an upcoming magnetizing 

interaction.


Coupling behavior in iron-oxide nanoparticle/Py thin film 

composite systems 

C. Fink 1 , P. Szary 1 , G.A. Badini Confalonieri 1 , D. Mishra 1 , L. Agudo 2 , G. Eggeler 2 , and 

O. Petracic 1 

1 Institut für Experimentalphysik/ Festkörperphysik, Ruhr-Universität Bochum, Bochum, Germany 

2 Institut für Werkstoffe, Ruhr-Universität Bochum, Bochum, Germany 

We report on the effect of dipolar coupling between ultrathin films of Permalloy 

and mixed-phase iron-oxide nanoparticles. 

Recently, a new class of materials where the 

building blocks are nanoparticles or nanocrystals 

came into the focus of scientific research 

due to their tunable structural, optical, magnetic 

and electronic properties [1]. In the 

present study, we continue the work presented 

in [2] and focus on different coupling behavior 

in iron-oxide nanoparticle / Permalloy thin 

film composite systems. 

The systems are composed of a 2.2 nm 

thick Permalloy (Py = Ni80Fe20) film coated 

with one monolayer of mixed-phase magnetite 

(Fe3O4) - wüstite (FeO) nanoparticles (NPs). 

The NPs are coated with an organic surfactant 

of oleic acid and exhibit inner particle exchange 

bias. For details on the sample fabrication 

please refer to [2]. A schematic and a transmission 

electron microscopy (TEM) image of 

the system is shown in Fig. 23. 

Fig. 23: Schematics of the different composite systems 

without (a) and with (b) an additional Al2O3 

layer. Panel (c) shows a TEM cross section image of 

the composite system. 

We prepared two different types of composite 

systems using iron-oxide nanoparticles purchased 

from Ocean NanoTech. In system A 

(Fig. 23 (a)), the NPs were deposited directly 

onto the Py. However, in system B (Fig. 

23 (b)) an additional sapphire (Al2O3) layer 

was introduced between the Py and the NPs 

-25- 

in order to reduce the effect of dipolar coupling. 

Magnetic behavior was characterized using 

superconducting quantum interference device 

(SQUID) magnetometry. For this purpose, 

first, the samples were cooled down in a small 

negative field of approximately -10 Oe. Then, a 

positive field of +50 Oe was applied and M(T ) 

was recorded during heating (ZFC*) and subsequent 

cooling of the sample (FC) (Fig. 24). 

The small negative cooling field was used in order 

to imprint a preference direction onto the 

magnetization of the Py layer and thus stress 

its contribution in the M(T ) curve. M(H) 

magnetic hysteresis curves were measured after 

field-cooling in 50 Oe (Fig. 25). 

Fig. 24: ZFC* and FC measurements of the different 

composite systems, i.e. for Py/NP (a) and 

Py/Al2O3/NP (b). 

In Fig. 24, the M(T ) behavior is shown for the 

Py/NP (a) and the Py/Al2O3/NP (b) system. 

It is a superposition of the contribution of the 

NPs and the Py layer. A steep increase of the


magnetization is observed in the ZFC* curves 

at ∼43 K in the Py/NP composite and at ∼13 

K (inflection points) in the Py/Al2O3/NP composite, 

respectively. The same effect has been 

observed in our previous investigations and can 

be explained by the reversal of the Py [2]. The 

lower temperature of the Py reversal in the 

Py/Al2O3/NP composite can be attributed to 

decoupling due to the Al2O3 spacer layer between 

Py and NPs. The second increase in 

the ZFC* curves describes the alignment of the 

NPs in the applied field. In the case of Fig. 

24 (a) we find the increase already appearing 

at ∼133 K. However, by introducing the sapphire 

layer, the step is shifted to ∼166 K (Fig. 

24 (b)). Moreover, a peak in the ZFC curve 

is observed at ∼185 K and ∼238 K for the 

Py/NP and the Py/Al2O3/NP system. These 

values have to be compared to a reference sample 

with only NPs (not shown). Here, we find 

this step at a temperature of ∼153 K and for 

the blocking temperature ∼224 K. Most probably, 

in Fig. 24 (a), the reversal of the Py layer 

influences the realignment of the NP’s magnetization 

due to the dipolar coupling and thus 

is responsible for the lower temperature compared 

to the reference sample. In contrast, the 

insulating layer leads to a strong decoupling of 

the Py and the NPs and therefore yields comparable 

characteristic temperatures of the ZFC* 

curve as in the reference NP-system. Moreover, 

the step in the FC curves observed at ∼111 K 

is due to the Verwey transition occurring in 

magnetite. 

Figure 25 (a) shows the hysteresis of the composite 

system without Al2O3. Here, we discover 

a decoupled, step-like reversal, first of the 

Py and then of the NPs. In panel (b) of Fig. 

25 (b) we find a strongly decoupled switching. 

The first step in the hysteresis, corresponding 

to the Py reversal is much smaller compared 

References 

[1] S.A. Claridge et al. ACSnano 3, 244 (2009). 

[2] P. Szary et al. Annual Report EP IV 2010 45-46 (2010) 

[3] G.A. Badini Confalonieri et al. Beilstein J. Nanotechnol. 1, 101 (2010). 

[4] M.J. Benitez, D. Mishra et al. J. Phys.: Condens. Matter, 23 126003 (2011). 

-26- 

to (a) and in the same range as for a reference 

Py layer without NPs (not shown) which supports 

the idea of a strong decoupling. The second 

step in (b) indicates switching of th NPs 

which occurs at similar field values as in (a). 

The small asymmetry and shift of the hysteresis 

for both systems can be explained by the 

inner-particle exchange bias. 

Fig. 25: Hysteresis loops of the Py/NP (a) and 

Py/Al2O3/NP (b) composite. 

In conclusion, we observe a weaker coupling 

of the composites compared to our previous 

study. In particular, the system with the additional 

sapphire layers shows an almost uncoupled 

behavior indicated by the small coercive 

field in the hysteresis and the almost similar 

characteristic temperatures in the ZFC* 

curve when comparing to the reference system. 

The authors would like to thank M. Bienek, A. 

Ludwig, A. Rai and A. Ludwig for technical 

help and the Materials Research Department 

of the Ruhr-Universität Bochum for financial 

support.


Structural and magnetic properties of self-assembled iron oxide 

nanoparticle superlattices 

D. Greving, G. A. Badini Confalonieri, D. Mishra, O. Petracic, and H. Zabel 

Ruhr-Universität Bochum, 44780 Bochum, Germany 

The substrate dependent growth as well as the resulting magnetostatic properties 

of iron oxide nanoparticle (NP) superlattices were investigated. 

Thin films of closely packed iron oxide NPs 

were prepared by spin coating. Two different 

types of substrates were used to investigate 

the substrate-dependent colloidal growth 

modes and the magnetostatic interactions in 

between the NPs. Particular attention was 

given to the so-called memory effect known 

from superspin glasses (SSGs) [2]. The NPs 

were purchased from Ocean Nanotech with a 

diameter of 20 nm. The particles consist of 

a mixture of a FeO (wüstite) and γ-Fe2O3 

(maghemite) phases. The phase composition 

of the NPs can be changed to mainly Fe3O4 

(magnetite) by an annealing treatment, i.e. 

heating up the samples to 120 ◦ C in air or 230 ◦ C 

in vacuum, respectively. The substrates used 

in this work were silicon and electropolished 

aluminum wafers. Using scanning electron microscopy 

(SEM) imaging, the NPs growth type 

was found to be strongly dependent on the substrate. 

Fig. 26: NPs spincoated on a Si substrate showing a 

Stranski-Krastanov growth mode. 

The self-organization of particles spincoated 

onto silicon can be described in analogy to 

thin film growth by the Stranski-Krastanov 

(SK) growth mode (Fig. 26). This mode is 

characterized by first building few complete 

and smooth layers covering the entire substrate 

which is then continued by island growth for 

the following layers. Consequently, this behavior 

is dominated by island growth for large 

-27- 

numbers of layers. Contrary to this, NPs on 

aluminum seemed to prefer a form of arrangement 

similar to Frank-van-der-Merwe (FvdM) 

growth (Fig. 27). It is characterized by smooth 

and complete layers one after another for all 

layers. 

Fig. 27: NPs spincoated on Al substrate showing 

Frank-van-der-Merwe growth mode. 

Strictly speaking, these models apply for films 

composed of atoms. However, it seems legitimate 

to assume that the same or similar 

physical mechanisms describing the growth of 

atomic films are also valid in the case of NPs. 

Recently, we succeeded to observe even the 

third growth mode, i.e. Volmer-Weber (VW) 

growth being characterized by complete island 

growth for all layers [3]. This is observed for 

NPs spincoated onto a layer of PMMA [3] 

Furthermore, the mean ’supergrain’ diameter, 

d, i.e. the area within which the self-organized 

NPs share the same lattice orientation, was obtained 

from analysis of several SEM images. 

We find: dSi = (149 ± 42) nm = (8.3 ± 2.8)dNP 

in the case of silicon and dAl = (185 ± 34) nm 

= (10.3 ± 1.9)dNP in the case of aluminum 

wafers, with dNP being the diameter of a single 

NP. Thus, we showed that, besides the different 

growth modi, the growth on silicon leads to 

smaller grain sizes. Consequently it then shows 

a worse degree of packing with more structural 

defects.


Fig. 28: Difference curve of two ZFC magnetization 

measurements of Fe-oxide NPs on Si substrate annealed 

at 80 ◦ C, one with a waiting time of 1000 s at 150 K, 

the other without. Pronounced bulge in ∆M vs. T 

is visible at the temperature of the waiting point Tw, 

indicative for a memory effect. 

These differences in the packing are supposed 

to influence also the magnetic behavior of 

an ensemble of NPs. Therefore, the samples 

were studied in Zero-Field-Cooling (ZFC) measurements 

as function of temperature using a 

SQUID magnetometer. A ZFC curve implies 

that a sample is cooled in zero field down to a 

temperature below the blocking temperature. 

Then, a magnetic field is applied and the magnetization 

M of the sample is recorded as a 

function of the increasing temperature T during 

warming up. 

The individual NPs used here show superparamagnetic 

(SPM) behavior. However, the films 

of NPs are expected to show SSG behavior. 

Therefore, two ZFC measurements were performed, 

one with a certain waiting time tw 

(e.g. 10000s) at an intermediate waiting temperature 

Tw (around 140-200K) during cooling 

down, and the other measurement without this 

waiting period. 

In the case of a SSG (and more generally in 

the case of a spin glass (SG)), halting the sys- 

References 

tem at a certain temperature Tw will ’age’ the 

system at this temperature and thus imprint 

a particular metastable spin state. This state 

is ’recalled’ upon reheating. The ZFC curve 

with waiting will show a dip exactly at T = Tw 

compared to the reference ZFC curve. This is 

known as the memory effect in SG systems [4]. 

The effect of the memory effect is better visible 

if the difference between ZFC curve and 

reference ZFC curve is plotted (Fig. 28). 

Fig. 29: Difference curves for ZFC magnetization measurements 

with and without waiting time as function of 

temperature for a magnetite sample annealed at 230 ◦ C 

in vacuum on Al substrate. 

Although the expected dips near Tw could easily 

be observed in the FeO-phase samples, the 

magnetite samples annealed at 120 ◦ C in air 

and 230 ◦ C in vacuum show a surprising oscillatory 

behavior around Tw on both Si and Al 

substrates (Fig. 29). These oscillations cannot 

clearly be attributed to the memory effect 

since no such behavior is known from literature. 

Further research is necessary. 

The authors acknowledge support by the Materials 

Research Department of the Ruhr- 

University Bochum, funding by the Rektorat of 

the Ruhr-University Bochum and by the state 

NRW. 

[1] D. Greving, Bachelor Thesis, Magnetostatic Interactions in Systems of Self-Assembled Iron Oxide Nanoparticles 

(2010) 

[2] O. Petracic et al., J. Magn. Magn. Mater. 300, 192 (2006); Superlatt. Microstr. 47, 569 (2010). 

[3] D. Mishra et al., Nanotechnology 23, 055707 (2012). 

[4] Spin Glasses and Random Fields, Ed. A.P. Young (World Scient., 1998), Vol. 12. 

-28-


An experimental approach to a 2-dimensional magnetic network 

close to the percolation transition 

M. Lange, P. Szary, O. Petracic, F. Brüssing, and H. Zabel 

Institut für Experimentalphysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany 

We prepared 2-dimensional networks by means of nanosphere lithography with different 

bridge widths. This enabled us to produce networks close to the percolation 

transition. On this networks magnetic and electrical investigations were performed. 

The present study combines the approaches of 

percolation transition and magnetic networks. 

In the focus of this study are network systems 

with narrow connections, i.e. small bridgewidths 

and thus networks close to the percolation 

transition. To our knowledge only few 

experimental studies exist to observe the percolation 

transition in networks [1; 2]. 

(a) 

(b) 

disconnected 

link 

backbone 

2 mm 2 mm 

Fig. 30: Scanning Electron Microscope (SEM) images 

of networks fabricated with nanosphere lithography in 

order to show hexagonal ordering (a) and typical defects 

(b): disconnected links and backbones. 

Different approaches to fabricate the networks 

were considered, whereby nanosphere lithography 

using micrometer-sized, self-assembled 

polystyrene spheres turned out to be the most 

capable method (compare [3]). For example, 

it allows the fabrication of networks with a 

very high lateral resolution compared to other 

methods (e.g. electron beam lithography) and 

provides a random ordering of the network. 

Self-organizing the spheres via the horizontal 

sliding method, enabled us to produce large 

and close-packed hexagonally ordered monolayers. 

By means of oxygen plasma etching the 

spheres were decreased in size in a controlled 

fashion and thus networks of different bridgewidths 

could be fabricated. Subsequently, the 

self-organized spheres were used as a shadow 

mask during the deposition of soft ferromagnetic 

Permalloy (Py) (compare Fig. 30). How- 

-29- 

ever, due to the self-organization and plasma 

etching process, defects could occur as shown 

in Fig. 30. 

Fig. 31: The specific resistance of the measured 

samples in dependence of the average bridge-width 

(red) and the estimated specific resistance for a sample, 

where the resistance was above the limit of the 

measurement setup (blue). 

The average bridge-width of each network was 

determined in a structural analysis and was 

used as the characteristic parameter for the 

subsequent studies (compare [4]). The magnetic 

and electrical behavior of the networks 

was studied by means of magneto-optical Kerr 

effect (MOKE) and magneto-resistance measurements. 

All samples were investigated in 

longitudinal and transverse geometry, i.e. current 

parallel and perpendicular to the external 

field, respectively. Moreover, the resistances 

of the networks at zero applied magnetic field 

were measured. With these values the specific 

resistances were calculated and plotted 

as a function of the bridge-width. This plot 

is displayed in figure 31 which shows the tendency 

of a percolation transition, i.e. an increasing 

specific resistance with decreasing average 

bridge-width. In the magnetic investigations 

we observed an increased value of the


coercive field of the networks compared to a 

continuous film because the antidot structure 

and the roughness induced by the plasma etching 

process lead to an increased number of pinning 

centers during the reversal process (compare 

[3]). Furthermore, all samples showed 

an anisotropic magneto-resistance and a large 

isotropic negative magneto-resistance due to 

spin order scattering. A characteristic property 

which was common to all samples is the 

occurrence of a double peak behavior in the 

anisotropic magneto-resistance. In figure 32 a 

magneto-resistance measurement is exemplary 

displayed for one network in longitudinal direction. 

Here, the first peak corresponds to an 

external field of 120 Oe and the second peak 

to 240 Oe. In order to understand the occurrence 

of the double peak, the switching fields 

of both peaks in the magneto-transport curve 

and the coercive field in the hysteresis curves 

obtained by MOKE were compared. It turned 

out that the field value of the first peak remains 

nearly constant for all samples, whereas the 

second peak increased with decreasing bridgewidth. 

This effect can be explained as an 

independent switching of defects (backbones) 

and the network. Figure 32 shows spin structures 

obtained by micromagnetic simulations 

of a network structure with a defect. The defect 

switches earlier than the residual network, 

which leads to two peaks in the anisotropic 

magneto-resistance curve. However, magnetic 

hysteresis curves obtained from MOKE measurements 

did not show any evidence of two 

different switching fields. Here, the measured 

coercive field for all samples was in between 

the field values of the two transport peaks, 

which is attributed to an effect of the different 

measuring techniques. In the case of magnetotransport 

measurements the main part of the 

current is going through the broader backbones, 

whereas no current passes the disconnected 

links. Thus, the backbones are of increased 

importance for the resistive behavior. 

However, MOKE averages over all magnetic 

parts of the sample, in particular also over 

those which are disconnected. This yields a 

magnetic hysteresis, where the backbones play 

a less crucial role than for the transport measurements 

and hence no second peak occurred. 

-30- 

The coercive field is an average of the entire 

sample and thus is in between the field values 

of the two peaks of the transport measurements. 

Fig. 32: Bottom: transport measurements of a Py network 

in parallel geometry. Top: spin-structure images 

of a network obtained from micromagnetic simulations. 

In order to get a deeper understanding of the 

effect of randomness in the network structures, 

a perfectly symmetric network, prepared by 

means of electron beam lithography, was investigated. 

Here, the bridge-width was constant 

over the entire sample. As expected, this network 

did not show any double peak behavior 

and supports the above given model. Moreover, 

in this perfect symmetry we could observe 

the occurrence of a six-fold anisotropy due to 

the hexagonal structure of the network. For 

a better comparison a network with a higher 

bridge-width could be fabricated by means of 

nanosphere lithography. In order to get a better 

understanding of the percolation transition 

and compare to theoretical models, more networks 

close to the threshold have to be prepared 

in future. Moreover, other measurement 

techniques (e.g. photoemission electron microscopy) 

would give a more detailed picture 

of the switching behavior. 

References 

[1] Parish, M. M. et al. Nature 426, 162 (2003) 

[2] Bunde, A. et al. Diffusion Fundamentals 6, 1 

(2007) 

[3] M. Lange et al. Annual Report, EP IV RUB (2010) 

[4] M. Lange Master Thesis, RUB (2011)

Epitaxial self-assembly of iron oxide nanoparticles 


D. Mishra 1 , D. Greving 1 , G. A. Badini Confalonieri 1,2 , P. Szary 1 , J. Perlich 3 , B. P. 

Toperverg 1,4 , O. Petracic 1 , H. Zabel 1 

1 Institut for Experimental Condensed Matter Physics, Ruhr University Bochum, Germany 

2 Instituto de Ciencia de Materiales, E-28049 CSIS Madrid, Spain 

3 HASYLAB at DESY, Notkestrasse 85, 22607 Hamburg, Germany 

4 Petersburg Nuclear Physics Institute RAS, Gatchina 188350, St Petersburg, Russia 

We report on self-assembly of iron oxide nanoparticles (NP) studied by SEM and 

GISAXS, which mimic the atomic thin film growth modes. 

The arrangement of NPs in 2- and 3-d close 

packed structures has opened up novel nanodevice 

fabrication processes with tunable electrical 

and magnetic properties [1; 2], which demand 

better understanding of the physical or 

chemical processes driving the NP ordering. 

We used iron oxide NPs (purchased from 

Ocean NanoTech LLC) of mean diameter 

(18 ±1.08 nm) dispersed in toluene for selfassembly. 

The substrates used were silicon (Si), 

and PMMA (with different molecular weights) 

coated silicon (PMMA 4P, PMMA 33P). The 

PMMA 4P and PMMA 33P substrates were 

prepared by spin-coating PMMA on Si at 4000 

rpm for 30 s and were heat treated at 80 ◦ C in 

air for 20 minutes. In the final step, NPs were 

spin-coated at 4000 rpm for 30 s on these substrates 

and were heat treated at 80 ◦ C in air 

for 20 minutes. In another experiment, selfassembly 

was achieved by sedimentation on 

PMMA 4P with excess of toluene. 

Fig. 33: GISAXS geometry 

Scanning electron microscopy (SEM) was used 

for real space characterization, while grazing incidence 

small angle x-ray scattering (GISAXS) 

was used for the reciprocal space map. The 

GISAXS patterns were measured at HASY- 

LAB beam line BW4 at a photon energy of 

-31- 

8.978 keV. The GISAXS images were captured 

by a MarCCD camera with 2048×2048 pixels 

and a pixel size of 79.1µm. The sample to detector 

distance was 210.44 cm, which gives an 

angular resolution of 0.00215 ◦ . The geometry 

of the GISAXS measurements is shown in Figure 

33. The angle of incidence was 0.5 ◦ . 

Fig. 34: SEM (a, b, c) and GISAXS (d, e, f) images on 

Si, PMMA 4P and PMM 33P substrates respectively. 

Figure 34a shows the SEM image of the NPs 

spin-coated on a Si substrate, a monolayer 

of NPs in hexagonal close packed (HCP) order. 

Figure 34b shows the SEM image on 

PMMA 4P. The NPs form 3-d islands of 1µm 

in size, separated by few hundred nanometers 

from each other. The NPs inside each island 

(inset of the figure), lack long range order. The 

NPs on PMMA 33P (Figure 34c) form a network 

of islands. The inset shows that the NPs 

are arranged in HCP structure. The GISAXS 

pattern for the NPs on Si (Figure 34d) has


two key features, the ring like intensity distribution, 

a manifestation of Fourier transform of 

the form factor of the NPs and the Bragg peaks, 

a manifestation of scattering function (Fourier 

transform of the pair-correlation function)[2]. 

The Bragg peak positions could be assigned to 

a 2-d HCP lattice with lattice constant 20.38 

nm. The GISAXS pattern on PMMA 4P (Figure 

34e) shows only broad rings without any 

in-plane Bragg peaks, due to the absence of 

any long range ordering inside the islands. The 

position of the ring matches with the intraparticle 

distance. The GISAXS pattern on 

PMMA 33P (Figure 34f) shows again a 2-d 

HCP lattice reflecting the polycrystalline like 

order inside the islands. 

The NP film formation reveals a striking similarity 

to the atomic thin film growth process. 

The 3 thin film growth modes are (a) 

layer by layer growth (Frank-van-der-Merwe/ 

FM growth), (b) island growth (Volmer- 

Weber/VW growth) and (c) layer plus island 

growth (Stranski-Krastanov/SK growth). 

In the atomic growth processes the different 

modes are basically driven by two parameters, 

namely lattice mismatch and surface interaction 

energy between the deposited material 

and the substrate. In the current scenario for 

NPs the first parameter could be neglected because 

the NP diameter is much bigger than 

the atomic lattice. So the deciding factor is 

the NP solution and film interaction energy, 

which shapes the film morphology. The two 

surface energies involved in the process are 

substrate-NP (γSN) and NP-NP (γNN) interactions. 

In a simple model, γNN < γSN implies 

FM growth, γNN > γSN implies VW growth 

and γNN = γSN implies SK growth mode. The 

NP growth on Si resembles FM growth, while 

that on PMMA 4P resembles VW growth. 

Figure 35a and b show the SEM images of the 

sedimentation samples. The NPs form nearly 

References 

[1] Whitesides et al., Science 295 2418 (2002) 

[2] Majetich et al., ACS Nano 5 6081 (2011) 

[2] Mishra et al., Nanotechnology 23 055707 (2012) 

-32- 

triangular islands (VW growth) and grow epitaxially 

inside each island. But the random 

orientation of islands give rise to a polycrystalline 

like GISAXS pattern (Figure 35c and 

d), indexed assuming a HCP lattice. The angle 

of incidence was 0.1 ◦ . The appearance of 

Bragg spots instead of Bragg rods is an indication 

of the 3-d extension of the lattice planes. 

Fig. 35: SEM (a, b) and GISAXS (c, d) images of 

sedimentation. 

Fig. 36: Line scan for sample (a) sedimentation at 

qz = 0.9nm −1 and (b) PMMA 33P at qz = 0.58nm −1 

with Lorentzian fits. 

The 1-d plot of intensity versus qy at a constant 

qz value for the sedimentation and PMMA 33P 

sample is shown in Figure 36a and b, respectively. 

The respective Lorentzian profile fits 

yield a coherence length of 280 ±6 nm and 100 

±4 nm. 

In summary, we succeeded in obtaining selfassembly 

of 18 nm NPs, resembling the atomic 

growth modes (FM and VW). The NP ordering 

inside the islands was found to be either 

polycrystalline, amorphous or single crystal. A 

complete theoretical modelling is in progress regarding 

the NP growth modes.


Polarized neutron reflectivity of monolayers of iron oxide 

nanoparticles at Super ADAM 

D. Mishra 1 , A. Devishvili 1,2 , O. Petracic 1 , G. A. Badini Confalonieri 1,3 , P. Szary 1 , 

K. Theis-Bröhl 4 , B. P. Toperverg 1,5 , H. Zabel 1 

1 Institut for Experimental Condensed Matter Physics, Ruhr University Bochum, Germany 

2 Institut Laue-Langevin, BP 156, F-38042 Grenoble, France 

3 Instituto de Ciencia de Materiales, E-28049 CSIS Madrid, Spain 

4 University of Applied Sciences Bremerhaven, D-27568 Bremerhaven, Germany 

5 Petersburg Nuclear Physics Institute RAS, Gatchina 188350, St Petersburg, Russia 

We report about Polarized Neutron Reflectivity (PNR) measurements of iron oxide 

nanoparticle monolayers spin-coated on a Vanadium film. 

The 2-d and 3-d self-assembly of magnetic 

nanoparticles (NPs) is promising for 

high density data storage and spintronics 

applications[1]. The pertinent question in 

dense assemblies is the arrangement of magnetic 

moments (superspins) due to the dipolar 

coupling between the NPs, which we have investigated 

by PNR. 

PNR from a monolayer sample is difficult 

to measure unlike a multilayer[2], because of 

small scattering volume of magnetic materials. 

To enhance the magnetic contrast of the 

film a different approach was used, where neutron 

standing waves were formed by sandwiching 

a material of negative potential between 

two positive potential materials[3]. The standing 

waves enhance the probability of scattering 

from the probing layer and increase the 

magnetic contrast. In our case a tri-layer system 

of NP/V /Al2O3 was used. The iron oxide 

NPs of 20 nm diameter were spin-coated 

on a sputtered V film (50 nm) on a-plane sapphire 

substrate. The PNR measurements were 

carried out at the Super ADAM reflectometer 

stationed at ILL Grenoble with λ of 0.441 

nm. The polarization efficiency was about 97%. 

All measurements were done at room temperature 

and all four channels of reflectivites were 

measured by a position sensitive 3 He detector 

(PSD). Figure 37 (a) and (b) show SEM images 

of nearly a monolayer film spin-coated on 

V at different positions of the sample. The images 

show hexagonal close-packed ordering and 

a discontinuous second layer could also be seen. 

-33- 

Figure 38 shows the geometry of the PNR measurements. 

The right panel shows the theoretical 

profile of the neutron potential well. 

Fig. 37: (a) and (b) SEM images of nearly one monolayer 

of iron oxide NPs. 

Fig. 38: PNR geometry, � ki the incident wave vector, 

�kf the exit wave vector, �qz scattering vector, � H external 

magnetic field parallel to the neutron polarization 

axis (Y-axis), � M Magnetization vector and γ angle between 

� M and � H. (b) The theoretical neutron potential 

well. 

Figure 39 (a) and (b) show the non spin flip 

(NSF) R ++ , R −− and spin flip reflectivites R +− 

and R −+ at high field (2 kOe) and remanence 

(8 Oe) respectively along with the fits (solid 

line). The spin asymmetry (R ++ - R −− )/ (R ++ 

+ R −− ) shown in Figure 39 (c) is an indication 

of the magnetized state of the sample at 2 

kOe, which disappears in remanence. Surprisingly 

no spin flip scattering was observed in 

remanence. For quantitative analysis, all four 

curves were fitted simultaneously, described by


following equations, 

R ++ = 1 

4 |R+(1 + cos γ) + R−(1 − cos γ)| 2 

R −− = 1 

4 |R+(1 − cos γ) + R−(1 + cos γ)| 2 

R +− = R −+ = 1 

4 |R+ − R−| 2 sin 2 γ 

where R+,− are the reflectance amplitudes for 

positive and negative spin projection of neutron 

on � M and γ is the angle between � M and 

neutron polarization ( � P )[4]. 

Fig. 39: PNR measurments (a) at high field (2 

kOe)(b) in remanence. The inset shows the nuclear 

SLD (Nb) profiles. (c) Spin asymmetry at 2 kOe and 

remanence along with the fit. 

The inset shows the nuclear SLD (Nb) values 

obtained from the fit. The top NP layer has the 

highest roughness, probably due to its incompleteness 

and some residual organics present 

on the top. Next comes the organic shell with 

a lower Nb followed by the second complete 

NP layer. The fitting parameters used are the 

Nb of NP layers, roughness and magnetic SLD 

References 

(Np) of all layers, cos γ and sin 2 γ. In remanence 

all thicknesses and Nb values were held 

fixed, same as obtained at 2 kOe. The value 

of cos γ at 2 kOe and in remanence are 0.35 

and 0.14 respectively, which reflects the deviation 

of � M from the fully saturated state, which 

should be along � H. 

The Np values obtained from the fitting at high 

field and remanence are shown in Figure 40 (a) 

and (b) respectively. It is surprising that the 

Np values per layer are not zero in remanence, 

although total magnetization is zero. This 

means that the magnetization persists over an 

area larger than the neutron coherence length, 

but over the whole film has a random orientation. 

One could imagine that the dipolar interaction 

leads to such magnetic correlation extending 

over few NPs. The sketches in Figure 

40 (c) and (d) show the superspin arrangement 

at 2 kOe and in remanence respectively. 

Fig. 40: Magnetic SLDs (Np) and sketch of superspin 

arrangement at 2 kOe ((a), (c)) and in remanence ((b), 

(d)) respectively. 

In summary we have succeeded in obtaining 

the nuclear and magnetic SLD profile of a 

monolayer of NP film by neutron standing 

wave formation. In remanence, dipolar coupling 

leads to the formation of local quasidomains 

over several NPs. 

We thank Mrs Sabine Erdt-Böhm for preparing 

vanadium films on sapphire substrates. 

[1] Murray et al., Annu. Rev. Mater. Res. 30, 545 (2000) 

[2] Mishra et al., Nanotechnology 23, 055707 (2012). 

[3] Ignatovich et al. Physical Review B 64, 205408 (2001). 

[4] Zabel et al. Handbook of Magnetism and Advanced Magnetic Materials 3,ed. H Kronmüller and S Parkin, 

New York: Wiley (2007). 

-34-


Magnetization reversal in dipolarly coupled PdFe nanodot arrays 

M. Ewerlin, D. Demirbas, F. Brüssing, O. Petracic and H. Zabel 


We have studied a 2-dimensional XY macrospin model system by fabricating nanodot 

arrays from Pd1−xFex with low Fe concentrations as magnetic material using 

electron beam lithography. The magnetization reversal of the entire system was 

studied using a low-temperature MOKE setup. 

Circular magnetic nanodots arranged on a periodic 

lattice are a potential realization of a 

2-dimensional XY system. Each single dot carries 

a macrospin if its size is below the single domain 

limit. Since the anisotropy of each dot is 

expected to be negligible, dipolar interactions 

between the macrospins might lead to a complex 

order of the entire system. To realize and 

investigate this experimentally we have fabricated 

single domain nanodots on a square lattice. 

As magnetic material we used an alloy of 

Pd1−xFex. The Curie temperature of such alloys 

depends on the Fe concentration and therefore 

can be tuned. We chose a Fe concentration 

of x=13% aiming a Curie temperature below 

room temperature. This low TC ensures that 

the system can be cooled from a completely 

paramagnetic state into the macrospin state. 

Fig. 41: SQUID measurements on a continuous film 

with x=13%. The m(T) curve is shown in a). The 

Curie temperature is estimated to be 290 K. b) shows 

a hysteresis measured at 100 K showing a very low coercive 

field of 0.8 Oe. 

The samples were prepared on Si substrates at 

room temperature using Ar ion beam sputtering 

at a base pressure better than 5 × 10 −9 

mbar. On top of a 5 nm Ta buffer layer a 10 

nm PdFe layer was sputtered from a Pd target 

covered partially with small iron stripes to 

achieve an iron concentration of x=13%. The 

-35- 

samples are capped with a 5 nm Al2O3 layer 

to protect them from oxidation. 

The magnetic characterization of the films was 

performed using superconducting quantum interference 

device (SQUID) magnetometry and 

is shown in figure 41. The m(T ) curve confirms 

a Curie temperature of 290 K and the 

hysteresis a coercive field of 0.8 Oe. 

Fig. 42: Phase diagram of nanodots simulated by 

OOMMF. The diagram shows the spin state in a single 

dot depending on the diameter and the thickness of the 

dot. The pink circle indicates the dots with d=150 nm 

and b=10 nm - which are realized in our experiments - 

showing a single domain state. 

OOMMF simulations were performed to generate 

a diagram showing the spin structure of 

a single dot depending on its diameter d and 

thickness b. Therefore the exchange constant 

A as well as the saturation magnetization Ms 

were determined using magnetization curves 

measured from continuous films0 at different 

temperatures via SQUID. The spin state was 

simulated for diameters between 60 and 900 

nm and b=5 nm, 10 nm and 20 nm, respectively. 

The phase diagram is shown in figure 

42. A clear separation between single domain


states and vortex states is shown, whereas in 

the single domain regime also s-state spin structures 

are included. For our experimental nanostructures 

we use dots with a thickness of 10 nm 

and a diameter of 150 nm, which show a clear 

single domain state (indicated with the pink 

circle in 42). The lithography was performed 

using negative resist and Ar ion milling. Figure 

43 shows a SEM image of the nanostructured 

samples. The dots are arranged on a square 

lattice with a periodicity of 300 nm. 

Fig. 43: SEM image of the nanostructured dots after 

milling. The dots have a diameter of 150 nm and are 

arranged on a square lattice with a periodicity of 300 

nm. 

The nanostructured sample was then measured 

in a low temperature MOKE setup. The hysteresis 

curves were taken for various temperatures 

down to 100 K. The results are shown 

in figure 44. Figure 44a) shows the hysteresis 

for 256 K, indicating that the system is below 

its Curie temperature and in a ferromagnetic 

state. With decreasing temperature the shape 

of the curves changes significantly. Down to 

160 K the hysteresis becomes vortex-like (see 

figure 44b) and c)), and for even lower temperatures 

the coercive field increases (figures 

44d) and e)). The hysteresis shows a singledomain-like 

shape at 100 K (figure 44f)). For 

temperatures between 250 K and 160 K the 

-36- 

spin structure of each dot is not purely single 

domain but s-shape or vortex-like. Due to 

dipolar interactions below a certain temperature 

around 150 K, the dots become single domain. 

Alternatively one might speculate about 

a state where the entire dot array forms a collective 

vortex-like state, which is temperature 

dependend. In this XY-Kosterlitz-Thouless 

scenario one would expect vortex-antivortex 

pairs which unbind and annihilate at the KTtransition, 

which would then be around 140 K 

in our case. Comparison with OOMMF simulations 

of interacting dots is expected to shed 

light onto this question. 

Fig. 44: Low temperature MOKE measurements at 

the PdFe dot array. a) - f) shows hysteresis curves for 

256 K, 185 K, 160 K, 150 K, 130 K and 100 K, respectively. 

The authors would like to thank Peter Stauche 

for technical support and the SFB491 for financial 

support.


Nucleation process of magnetic domains in Co2MnGe-Heusler 

nanostripes 

K. Gross, K. Westerholt, and H. Zabel 

Institut für Experimentalphysik/Festkörperphysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany 

Nucleation process of magnetic domains in Co2MnGe-Heusler nanostripes with different 

magnetocrystalline anisotropy are investigated by magnetic force microscopy 

(MFM), magneto-optical Kerr effect (MOKE) and by micromagnetic simulations. 

Recent developments of magneto-electronic 

devices require a good understanding of domain 

structures and magnetization reversal 

processes of nano-sized elements. Reversibility 

in the switching processes and stability 

of the remanent states are fundamental requirements 

for technological applications[1]. 

We study stripes prepared from the Heusler 

alloy Co2MnGe with a thickness of 100 nm 

prepared by rf-sputtering on (11¯20) Al2O3 

substrates; this Heusler phase can develop 

different in-plane anisotropies depending on 

the growth conditions. We investigate two 

different Co2MnGe films, the first one (designated 

as cubic sample) exhibits a pure cubic 

anisotropy with K4 = 1.2 ∗ 10 3 J/m 3 , the 

second one (uniaxial sample) has an uniaxial 

anisotropy with KU = 2.8 ∗ 10 3 J/m 3 . Using 

electronbeam- lithography and ion beam 

milling, the Co2MnGe films were shaped 

into rectangular slabs with the aspect ratio 

length/width = m = 17, 10, 7 and 5. The long 

axis of the stripes was oriented perpendicular 

to the uniaxial anisotropy axis. 

Fig. 45(a) shows MFM images of the fluxclosure 

domains obtained in zero field after 

saturation parallel and perpendicular to the 

stripe axis; in most cases (m = 17, 10 and 7) 

the equilibrium domain states are essentially 

independent of the orientation of the field. The 

domain size is determinate by the anisotropy 

and aspect ratio of the stripes as shown in 

the Fig. 45(b). Magnetization reversal of an 

array of stripes with m = 7 of the uniaxial 

sample was investigated by MOKE. Hysteresis 

loop for the field direction parallel to the stripe 

axis is shown in Fig. 46(a). The shape of the 

loop, together with the MFM images taken 

-37- 

at different positions along the hysteresis loop, 

evidence that the magnetization reversal of 

the stripes occurs trough a combination of domain 

-nucleation, -propagation, -rotation and 

-annihilation. 

Fig. 45: (a) Zero field magnetization configuration after 

saturation parallel and perpendicular to the stripe 

axis for the uniaxial sample. (b) Dependence of the 

domain width on the aspect ratio. 

Starting from the dipole state in saturation 

and by reducing the magnetic field, domain 

walls begin to nucleate at the nucleation field 

Hn= 36 mT; the nucleation begins at the ends 

of the stripes and subsequently domain walls 

start to propagate to the center and fill entirely 

the stripe. Then, at the lower rotation field HR 

= 6 mT, further reversal occurs trough continuous 

rotation of the domains until the vortices


are expelled at the annihilation field Ha = -36 

mT. Such switching modus was confirmed by 

OMMFF simulations (Fig. 46(b)). The calculated 

hysteresis loop is in good qualitative 

agreement with the experiment; however, the 

simulated chracteristic fields Hn = 20 mT and 

Ha = -16 mT are smaller as the experimental 

ones. Additionally, rotations at low fields 

are perfectly reversible, whereas in the experimental 

curve a small remanence and hysteretic 

behavior is seen. This disagreement is probably 

due to pinning of domain walls which give 

rise to a higher Ha. 

Fig. 46: MOKE (a) und simulated (b) hysteresis loops 

with the magnetic field applied along to the long axis 

of the stripes for m = 7(anisotropic sample). 

A different switching mechanism was observerd 

for fields applied in the perpendicular direction. 

In this orientation the nucleation of all 

domain walls starts simultaneously along the 

total stripe length. Subsequently, the domain 

walls propagate until they reach a fully compensated 

state at remanence. This process 

starts at different values of Hn depending on 

the width of the stripes. Narrower elements 

like the cases m = 17 and 10 start the switching 

first, as evidenced in the MFM image taken 

at H = 55 mT (Fig. 47(a)). At H =18 mT nucleation 

also appears in the stripes with m = 7 

and 5. The dependence of Hn on the aspect ratio 

for the cubic- and uniaxial-system is shown 

in Fig. 47(b). 

-38- 

Simulated and experimental hysteresis loops 

of the cubic sample (not shown) proved that 

the remagnetization follows steps similar to 

the uniaxial sample, however, it exhibits a 

non-zero remanence characterized by noncompensated 

metastable states strongly depending 

on the magnetic history. 

In conclusion, we studied domain configurations 

and the magnetization reversal of 

Co2MnGe-micro-sized stripes with different aspect 

ratios and magnetocrystalline anisotropy. 

Magnetic history plays an important role for 

the stripes with low cubic anisotropy but is 

essentially irrelevant for the sample with the 

low uniaxial anisotropy. In this respect the 

uniaxial sample is similar to the stripes with 

higher uniaxial anisotropy which we studied 

previorsly in [2]. 

Fig. 47: (a) MFM images of domains nucleation states 

at perpendicular fields H = 55 mT and 18 mT for the 

uniaxial sample. (b) Dependence of Hn on m for the 

cubic and uniaxial sample. 

Thanks are due to S. Erdt-Boehm and P. 

Stauche for collaboration in fabrication and 

technical support; to DAAD and the SFB 491 

for financial support. 

References 

[1] Stuart S. P. Parkin, et al., Science 320, 190 (2008) 

[2] K. Gross, et al., Phys. Rev. B 84, 054456 (2011)


Probing periodic permalloy stripe patterns with polarized neutron 

reflectometry 

D. Gorkov 1 , K. Zhernenkov 1 , B.P. Toperverg 1 , A. Vach 2 , C. Bock 2 , U. Kunze 2 and H. Zabel 1 

1 Institut für Experimentalphysik IV,Ruhr-Universität Bochum, 44780 Bochum, Germany 

2 Department of Electrical Engineering and Information Technology, Ruhr-Universität Bochum, 

44780 Bochum, Germany 

With polarized neutron reflectivity we have examined Py stripe patterns. The 

in-plane and out-of plane structure of the pattern was determined via quantitative 

analysis of specular reflection and off-specular scattering measured with two complementary 

orientations: with stripes perpendicular and parallel to the incident 

beam. In the first case Bragg scattering was recorded in magnetic fields applied 

along stripes. In the second case a saturating magnetic field of 1 kOe was directed 

perpendicular to the stripes and strong polarization dependent diffuse off-specular 

scattering was observed. It can be attributed to, e.g. stray fields created due to 

the appreciable roughness of the stripe edges. 

Lateral patterning of thin film surfaces is routinely 

used to modify their magnetic properties 

aiming to fulfill various requests for further 

design and engineering of micro and nanodevices. 

For instance, micro stripes of magnetically 

soft and isotropic material, such as 

permalloy, induce in thin films macroscopic uniaxial 

anisotropy. It is clear that the strength 

of such anisotropy depends on the hight and 

width of the stripes, as well as on the distance 

between them. However, it may also be quite 

sensitive to the degree of the stripe perfection. 

Indeed, magnetic moments of homogeneously 

magnetized narrow stripes with ideal edges 

would effectively interact via dipolar fields at 

their free ends at the sample boundary. This 

may not be the case for stripes with sufficiently 

rough edges. Then magnetic flux may not propagate 

along the total stripe length, but percolate 

into inter-stripe space, and hence affect 

neighboring stripes wherever the internal field 

homogeneity is sufficiently perturbed by the 

roughness. In fact, roughness induces interstripe 

interaction which may substantially reduce 

the net shape anisotropy. Moreover, imperfection 

of stripe boundaries may play a role 

of notches where domains are efficiently pinned, 

and/or nucleated during re-magnetization processes 

under alternating external field. This 

may increase the coercivity of the system be- 

-39- 

yond that is expected due to simply the geometrical 

factor[1]. 

� f 

� f 

2 0 

1 0 

0 

2 0 

1 0 

0 

N o r m a liz e d In te n s ity 

0 .1 

0 .0 1 

1 E -3 

1 E -4 

1 E -5 

s p in s u p 

s p in s d o w n 

0 1 0 2 0 

� i 

s p in s u p s im u la tio n 

s p in s d o w n s im u la tio n 

0 1 0 2 0 3 0 

1 E -6 

0 .0 0 0 .0 1 0 .0 2 0 .0 3 

� �� r a d i 

0 .0 4 0 .0 5 0 .0 6 

� i 

R + 

R - 

R + fit 

R - fit 

0 .0 1 3 0 0 

0 .0 0 5 2 0 2 

7 .9 4 6 E -0 4 

1 .9 9 8 E -0 4 

5 .0 3 9 E -0 5 

1 .2 8 6 E -0 5 

1 .0 0 0 E -0 6 

Fig. 48: (top row) Scattering intensity maps together 

with model calculation, (bottom)specular reflectivity 

curves together with fit to the experimental data 

The sample with the size of 20x20 mm 2 consisting 

of Py stripes was manufactured in the Engineering 

Department of the Ruhr-University


Bochum by use of laser lithography and lift-off 

technology with subsequent chemical etching. 

The individual stripes have a width of 1.1µm 

and periodicity of 4µm. Scanning electron microscopy 

confirmed almost perfect quality of 

the periodic pattern with small, but distinguishable 

roughness of the stripe edges. PNR 

experiments have been conducted at the Super- 

ADAM reflectometer at the ILL (Grenoble, 

France)[2]. The results of our first experiment 

are presented Fig.48. Two scattering maps for 

spins up and spins down state are shown for 

stripes oriented perpendicular to the scattering 

plane and parallel to the polarization direction. 

Diagonal ridges on the maps represent 

the specular reflection from mean optical 

potential, while curved bands indicate Bragg 

diffraction from periodic structure with the lateral 

period 4µm [3]. The bottom panel reproduces 

the specular reflectivity, where the Kiessig 

fringes from the layer thickness are well recognized. 

The reflectivities for up and down polarized 

neutrons are shifted against each other, 

indicative for the well magnetized state of the 

ferromagnetic Py - stripes. Right panels show 

results of the theoretical simulations based on 

the parameters deduced from the fit of reflectivity 

curves to the model. From the fit it follows 

that in the external field of 100 Oe the 

layer induction containing stripes is equal to 

3.05 kGauss. In our second experiment we rotated 

the stripes by 90 0 , so that the incident 

beam is directed parallel to stripes, see Fig.49. 

From fits we determined the filling factor to be 

around 0.4. Simultaneously, stripe magnetic 

induction of 11 kGauss was determined in saturating 

field of 1 kOe applied perpendicular to 

stripes. Multiplying 11 kGauss by the factor 

0.4 one obtains 4.4 kGauss for the film magnetic 

induction. This value exceeds by 30% the 

experimentally determined magnetic induction 

for the parallel case after saturating in a field 

of 100 Oe. From this we conclude that an external 

field of 100 Oe applied along the stripes 

is not sufficient for full saturation and the sample 

remains in a multi-domain state. Hysteresis 

loop measured later along and across stripes 

has shown that in the first case the saturation 

field is above 100 Gauss , while in the second 

case sample is saturated in the field of about 

1 kGauss. This value of 100 Oe is much higher 

than the usual coercivity of bulk Py or continuous 

Py films, which is around of few Oe. 

Thus the coercivity of the stripes is enhanced. 

One may ascribe this to residual domains heavily 

pinned by rough edges of stripes. With 

PNR we cannot detect this roughness seen otherwise 

with the electron microscopy. However, 

roughness may create extensive stray fields in 

the inter-stripe space hence generating spindependent 

off-specular scattering. The latter 

is depicted in Fig.49 for stripes oriented along 

the incident beam. In this case scattering from 

stray fields is enhanced due to Yoneda effect 

at the angles of total reflection from the Si substrate, 

but not from the stripe material as seen 

in Fig. 1. This strongly suggests that magnetic 

induction between stripes seen in specular 

PNR is laterally inhomogeneous. From the 

fit the size of inhomogeneities is estimated to 

be in the order of few µm. 

Fig. 49: Off-specular scattering intensity maps in a 

field of Hext = 1kGauss for stripes oriented parallel 

to the scattering plane (top row). Specular reflectivity 

curves together with the best fit to the experimental 

data (bottom row) 

References 

[1] M.T.Bryan, D. Atkinson and R.P.Cowburn, Journal 

of Phys., Conference Series 17, 40 (2005) 

[2] A. Devishvili, K. Zhernenkov, B. P. Toperverg, B. 

Hjorvarsson and H. Zabel, to be submitted Rev. 

Sci. Inst 

[3] H. Zabel, K. Theis-Bröhl, B. Toperverg, In Handbook 

of Magnetism and Advanced Magnetic Materials 

by H. Kronmüller/ S. Parkin (Eds.), Wiley 

p. 1237 (2007). 

-40-

Dynamic Processes 

FERROMAGNETIC NON- 

MAGNETIC 

FERROMAGNETIC 

~Bz 

~M1 

Spin Current 

Co Cu 

Ni81Fe19 

-41- 

~Bz 

~M2 


~M2


-42-


Time and element resolved magnetisation dynamics of ferrimagnetic 

GdFe in transmission geometry 

R. Abrudan 1 , I. Radu 2 , R. Weber 3 , K. Holldack 3 , R. Schumann 4 , M. J. J. Vrakking 4 , M. 

Weinelt 5 , H. Zabel 1 , and F. Radu 3 

1 Experimentalphysik IV,Ruhr-Universität Bochum, 44780 Bochum, Germany 

2 Institute for Molecules and Materials, Radboud University Nijmegen, 6525 ED Nijmegen, The Netherlands 

3 Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489 Berlin, Germany 

4 Max-Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, 12489 Berlin, Germany 

5 Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin 

A femtosecond laser pump-pulse is used to quench the magnetisation of ferrimagnetic 

GdFe alloy exhibiting perpendicular anisotropy. The effect is probed by 

circularly polarized synchrotron light synchronized with the fs-laser pump. 

ALICE chamber [1] is a diffractometer with 

a fully rotatable magnetic field and a sample 

temperatures between 10K - 475 K. X-ray 

Magnetic Resonant Scattering (XMRS), Total 

Electron Yield (TEY) in absorption and transmission 

and Fluorescence Yield (FY) measurement 

techniques are routinely used. Moreover, 

magnetization dynamics experiments involving 

a specially designed sample holder in order to 

use a pulsed magnetic field as excitation were 

demonstrated[4; 3]. 

Here we report on the successful implementation 

of laser-pump / X-ray probe technique using 

the Max-Born Institute Femtolaser facility 

in combination with the Alice diffractometer. 

We use the Femtosecond laser for pumping 

and resonant soft x-rays for probing the transient 

magnetization state with ∼ 50 ps resolution 

provided by the usual multibunch operation 

mode of the BESSY II synchrotron facility. 

The XMCD and XRMS in a transmission geometry 

are measured using single-photon counting 

technique: a PicoQuant electronic unit is 

triggered by the laser trigger which is further 

synchronized with the x-ray pulses. 

As a result the measured temporal spectra 

consists of a number of single bunch peaks. 

A sequence of the measured bunch is shown 

schematically in Fig 50. 

We have implemented three new detectors 

which were placed on the former detector arm. 

One avalanche photo-diode (APD1) is covered 

by Al foils to prevent laser reflections reaching 

-43- 

the active area. A second detector (APD2) is 

left wide open to measure the laser beam. By 

plotting the separate detection of the laser and 

x-ray beams we are able to control accurately 

the temporal overlap between the ”pump” and 

the ”probe” pulses. 

The size of the laser beam is one important 

parameter in this experiment and it needs to 

be reduced and focused on the sample surface 

using an optical telescope. 

Fig. 50: Schema of the time overlap used in the experiment 

(top). Delay scans measured for 100 mW Laser 

power on three independent x-ray bunches. (buttom) 

We were able to obtain a focused laser beam 

of about 100 µm in diameter which is slightly 

larger as compared to the x-ray beam (∼ 60 

µm).


Fig. 51: Fluence dependence of the XMCD signal 

measured at Fe L3. Lines represents fittings using a 

double exponential function [4].The corresponding fluences 

are: 4, 7, 10, 14 mJ/cm 2 for 30, 50, 70 and 100 

mW, respectively. Laser repetition rate was set here to 

30 kHz. 

Figure 50 shows a sketch of the time overlap 

used in this experiment; three temporally separated 

single bunches are measured simultaneously 

while the laser is delayed using a optical 

delay stage in order to scan across the middle 

x-ray bunch. At each point in time, the magnetic 

field perpendicular to the sample surface 

is switched between positive and negative values, 

this way avoiding any background problem 

due to the incoming beam decay. A representative 

delay scan is shown in Fig. 50 bottom; the 

red curves are recorded on the bunch prior to 

the pumped one (t=-1) and gives a measure of 

the XMCD signal similar to the static XMCD 

signal of the sample. The orange is the signal 

recorded on the later bunch after the pumped 

one (t=+1). Interestingly, the total XMCD signal 

is now reduced showing that the system is 

not relaxed completely and thermal effects persist 

more then 800 ns. Blue curves depicts the 

pumped signal (t=0) with a laser fluence of 14 

mJ/cm 2 . Left part of the curves is measured 

when the laser is still far away in time from 

the x-ray bunch, thus the XMCD signal is in 

fact the same as the static one (or the previous 

not pumped bunch one) and is getting reduced 

when the laser is temporarily overlapping the 

x-ray bunch. In this particular case the demagnetisation 

is closed to 100% , as the XMCD is 

now reduced to zero. 

Figure 51 depicts the laser fluence dependence 

of the XMCD. The curves show the signal measured 

on the pumped x-ray bunched and nor- 

-44- 

malised to the not-pumped one. A clear dependence 

of the magnetic signal due to the increased 

laser power is visible here. At t0 where 

the laser is temporarily perfect overlapped with 

the x-ray one can notice a drastic decay of the 

XMCD signal. At higher delays, the XMCD 

tends to relax back to the initial value at negative 

delays. For a 100 mW laser power, the 

XMCD (as can be seen also in the Fig. 50) is reduced 

to almost zero and the relaxation time 

is rather long. If one sets the Laser delay at 

positive delays close to t0 value and sweeps the 

magnetic field, three hysteresis loops on each 

bunch can be recorded. 

Fig. 52: Dynamic hyseresis loops measured on three 

different x-ray bunches, one of them being the pumped 

one (blue). 

Figure 52 shows three hysteresis loops measured 

at the 50 mW laser power. A reduction 

of the saturation magnetisation is clearly visible 

for the pumped signal in comparison with 

the un-pumped ones. These results demonstrates 

that the Alice diffractometer with the 

Max-Born Femtosecond facility can be used at 

HZB for pump-probe magnetisation dynamics 

in an usual multibunch operation mode of the 

synchrotron. 

We gratefully acknowledge the support provided 

by HZB and BMBF Contract No. 

05K10PC2. 

References 

[1] J. Grabis et al. Rev. Sci. Instr. 74, 4048 (2003) 

[4] St. Buschorn et al. J. Phys. D: Appl. Phys. 44 

165001 (2011) 

[3] R. Salikhov et al. Appl. Phys. Lett 99 092509 

(2011) 

[4] I. Radu et al. Nature 472 205 - 208 (2011).

Time-resolved XRMS in F/N/F trilayers (part I) 


R. Salikhov 1 , R. Abrudan 1 , F. Brüssing 1 , D. Mishra 1 , Ch. Luo 1 , F. Radu 2 , I. A. Garifullin 3 

and H. Zabel 1 

1 Ruhr-Universität Bochum, Germany 

2 Helmholtz Zentrum Berlin für Materialien und Energy, Berlin, Germany 

3 Zavoisky Physical-Technical Institute, Kazan, Russia 

We have found that the magnetic moments of Fe in permalloy layers in Co/Cu/Ni81Fe19 

trilayers exhibit different dynamical behavior in parallel orientation of the magnetization 

of the Py and Co layer, as compared to their antiparallel orientation. 

Spin current related phenomena in F1/N/F2 

structures, where F is the ferromagnetic layer 

and N is the normal metal layer are an important 

aspect of modern magnetism and can be 

treated in many different practical applications. 

For example, one can apply a spin-polarized 

electron current through the interface between 

the F1 and N layers to observe the magnetization 

torque in F2 layer that can lead to magnetization 

reversal of the F2 [1]. At the same 

time the inverse effect can be obtained, namely, 

a spin current can be created by a precession 

of the magnetization in an externally applied 

magnetic field. This inverse (spin pumping) effect 

may also lead to practical applications like 

a spin battery operated FMR [2]. 

J.-V. Kim and C. Chappert [3] theoretically 

investigated the dynamical coupling between 

magnetic moments of ferromagnetic layers by 

the spin-pumping effect in F1/N/F2 structures 

and concluded that this coupling can lead to 

configurational dependence of magnetic relaxations. 

That can give a unique possibility to 

control the relaxation rate of F2 layer by adjusting 

the magnetization direction of F1 and 

F2 layers to be parallel or antiparallel. 

We have studied Co/Cu/Ni81Fe19 (Py) trilayers 

with different thicknesses of Cu-spacer layers 

(25 and 40 nm) using the Time-Resolved 

X-ray Resonant Magnetic Scattering (TR 

XRMS) at the synchrotron radiation facility of 

the Helmholtz Zentrum Berlin (ALICE chamber). 

This method enables the detection of the 

free precessional decay of the magnetization of 

ferromagnetic films in response to a field pulse 

(for details see [4]). Samples were grown on sap- 

-45- 

phire (Al2O3) substrates by magnetron sputtering 

under a static magnetic field of about 1000 

Oe to induce a uniaxial magnetic anisotropy in 

ferromagnetic films. A 65 nm thick Cu conductive 

layer was deposited before the deposition 

of Co/Cu/Py systems. Current pulse through 

this Cu-layer generates a pulsed Oersted field 

Hp. For both samples the thicknesses of the 

Co and Py layers were 10 and 25 nm, respectively. 

The 350 µm wide stripe shaped samples 

were lithographically fabricated such that the 

magnetic easy axis is parallel to the stripe axis. 

TR-XRMS was measured at room temperature 

for parallel (P) and antiparallel (AP) orientations 

of magnetizations of the Co and Py-layer 

in our samples. In Fig. 53 we plot the magnetization 

precession of Fe in the Py layer for 

P (black open circles) and AP (blue closed 

circles) orientations in the Co/Cu(40 nm)/Py 

sample and for an external magnetic (bias) 

field HB = 11 Oe (a-b) and 13 Oe (c-d), which 

was applied along the easy axis. In both cases a 

decrease of the precessional relaxation time in 

the Py-layer upon transition from the P to AP 

state is clearly seen. From the fits we derive a 

noticeable increase in the Landau-Lifshitz (LL) 

damping parameter λ/4π from 190 ±20 MHz 

for the P orientation to about 270 ±30 MHz for 

the AP orientation. The damping parameters 

are essentially identical for both samples with 

different Cu spacer layer thicknesses. Here we 

would like to stress that the precessional frequency 

of the Py magnetic moments does not 

change from P to AP and equals 90 GHz and 

92 GHz for HB = 11 Oe and 13 Oe, respectively. 

This fact indicates that the stray field 

from domain walls of the Co layer does not


Opening Angle [deg] 

13 

12 

11 

10 

9 

8 

13 

12 

11 

10 

9 

8 

8 

7 

6 

5 

8 

7 

6 

5 

P 

AP 

(a) 

H B =11 Oe 

(b) 

H B =11 Oe 

(e) 

H B =21 Oe 

1 2 3 

Delay Time [ns] 

(f) 

H B =19 Oe 

4 

1 

AP 

P 

2 3 

Delay Time [ns] 

Co(10nm)/Cu(40nm)/Py(25nm) 

T=300 K 

(c) 

H B =13 Oe 

(d) 

H B =13 Oe 

-40 -20 0 20 40 

H [Oe] 

Fig. 53: Comparison of the magnetization dynamics 

of Py layer in the Co/Cu(40 nm)/Py sample measured 

for the P (black open circles) (a, c) and AP (blue closed 

circles) (b, d) mutual orientations of Co and Py magnetization. 

(e, f) represent delay scans for the P state 

with different signs of the magnetization direction (positive 

(e) and negative (f), see corresponding arrows in 

the hysteresis loop (g)). Solid lines represent the fits. 

strongly contribute to the change in damping 

parameter for P and AP configurations. (The 

effect of the domain wall stray fields from F1 

layer on magnetization dynamics of F2 layer 

in F1/N/F2 structures is described in detail 

in the next report). Moreover, we found that 

as magnetic moments in the Co layer reverse 

their direction along the descending branch of 

the hysteresis loop from P configuration in positive 

field to P configuration in negative field, 

the free precessional oscillation of the Py magnetic 

moments remains essentially the same 

(see Fig. 53(e and f) and hysteresis loop in (g)). 

This fact proves in addition that the observed 

change of precessional damping of the magnetization 

in Py is indeed intimately connected 

with the mutual orientation of the magnetic 

moments in the Co and Py layers and possible 

stray field inhomogeneities that may emanate 

from the Co layer do not affect strongly the 

spin dynamics in the Py layer. 

At low temperature the coercive field of the 

Co layer increases (see Fig. 54 (a)) giving possibility 

to compare the values of LL damping 

parameter for P and AP configurations in a 

higher range of the HB up to 38 Oe. TR- 

XRMS measurements of our samples at 100 K 

P 

f 

b 

AP 

a 

c 

e 

AP 

Py 

Co 

d 

4 

P 

(g) 

10 

9 

8 

7 

10 

9 

8 

7 

5 

0 

-5 

Opening 

Angle [deg] 

M [x10 -5 

emu] 

-46- 

show that the LL damping parameter for this 

range of HB remains different for P and AP 

orientations of magnetizations of the Co and 

Py-layer in our samples (Fig. 54 (b)). 

�� 

λ/4π [MHz] 

�� 

�� 

� 

�� 

�� 

�� 

�� 

�� 

�� 

�� 

�� 

�� 

�� 

�� 

�� 

�� 

� 

�� 

�� 

� � �� 

Fig. 54: (a) Hysteresis loop for Co/Cu(40 nm)/Py 

sample measured at 100 K. (b) LL damping parameters 

as a function of the bias field, measured at 100 K 

at P (black open circles) and AP (blue closed circles) 

mutual orientations of Co and Py magnetization. 

Taking into account the possible mechanisms 

which can cause the observed effect in our 

samples with relatively thick Cu-spacer layers 

where the exchange interaction between Flayers 

is negligible, we suggest that the increase 

of damping in Py for AP orientation of Co and 

Py magnetic layers is associated with the spinpumping-induced 

damping effect as it was predicted 

theoretically by J.-V. Kim and C. Chappert. 

We kindly acknowledge Peter Stauche for technical 

support. This work is supported by 

BMBF 05K10PC1. We are also thankful to 

the Helmholtz Zentrum Berlin for travel support 

under BMBF 05 ES3XBA/5. 

References 

[1] J. C. Slonczewski J. Magn. Magn. Mater. 159, L1 

(1996); L. Berger, Phys. Rev. B 54, 9353 (1996). 

[2] A. Brataas, et. al. Phys. Rev. B 54, 9353 (1996). 

[3] J.-V. Kim, C. Chappert J. Magn. Magn. Mater. 

286, 56 (2005). 

[4] St. Buschhorn, F. Brüssing, R. Abrudan, and H. 

Zabel J. Synchrotron Rad. 18, 212 (2011); J. Phys. 

D 44, 165001 (2011). 

� 

�� 

�� 

�� 

��

Time-resolved XRMS in F/N/F trilayers (part II) 


R. Salikhov 1 , R. Abrudan 1 , F. Brüssing 1 , K. Gross 1 , Ch. Luo 1 , F. Radu 2 , I. A. Garifullin 3 , 

K. Westerholt 1 and H. Zabel 1 




We have investigated the influence of the domain wall induced coupling effect on 

the precessional dynamics of Py layer in Co2MnGe/V/Py trilayers by TR-XRMS. 

In our previous report we presented the results 

of our study of Co/Cu/Ni81Fe19 (Py) spin valve 

systems by TR-XRMS, where we obtain a noticeable 

decrease of the precessional relaxation 

time in the Py-layers upon transition from the 

parallel (P) to the antiparallel (AP) state. We 

attributed our finding to configurational properties 

of the spin-pumping coupling of two ferromagnetic 

(F) layers separated by nonmagnetic 

metallic layer. Here we show that in certain 

cases the domain-wall (DW) induced coupling 

mechanism can also be responsible for 

the orientational dependence of the damping 

of free F-layer in spin valve systems. Origin of 

this mechanism is the magnetostatic coupling 

of the ferromagnetic thin layers at interfaces 

via DW stray fields [1; 2]. We also show that 

experimentally these two cases may be distinguished 

analyzing the precessional frequency 

for P and AP configurations of magnetizations. 

The Co layer in Co/Cu/Py samples is not fully 

saturated (see Fig. 55 (a)) even at the maximum 

bias field HB=80 Oe we can apply in our 

experimental setup. Therefore one can think 

that inversion of the magnetization direction of 

the Py and Co layers may cause a reconstruction 

of the size and shape of domains in the 

Co layer via the DWs induced coupling effect. 

Such reconstruction, in turn, may lead to an increase 

of the inhomogeneity of stray fields from 

the Co DWs at the Py layer. Inhomogeneity 

of stray fields, in turn, leads to higher values 

of the damping parameter and to a change in 

precessional frequency of the magnetization of 

Fe moments in Py layer. However, we showed 

experimentally that the latter remains equal 

for both configurations. This means that the 

influence of the DW induced coupling on the 

-47- 

magnetization dynamics in Co/Cu/Py system 

is negligible. 

In this report using our TR-XRMS setup we 

show that for another spin valve like system 

(Co2MnGe/V/Py trilayers) DW induced coupling 

mechanism dominates the precessional relaxation 

time when changing the mutual orientation 

of magnetizations. The samples for this 

study were grown by rf -sputtering at a substrate 

temperature of 300 o C on Al2O3 a-plane, 

for details of the Co2MnGe Heusler alloy growing 

see e.g. [3]. Here we used V (40 nm) buffer 

layer as a conductor for the current pulses. 

The magnetic hysteresis loop measured for 

the Co2MnGe(30 nm)/V(20 nm)/Py(15 nm) 

sample is shown in Fig. 55 (b). From the 

shape of the hysteresis loop one can conclude 

that the Co2MnGe layer reverses it’s magnetization 

direction via multiple intermediate domain 

states in contrast to the Co layer in 

Co/Cu/Py system Fig. 55 (a). 

M ( x 1 0 -5 e m u ) 

1 0 

5 

0 

-5 

-1 0 

5 

0 

-5 

(a ) 

T = 3 0 0 K 

(b ) 

T = 3 0 0 K 

C o (1 0 n m )/C u (2 5 n m )/P y (2 5 n m ) 

C o 2 M n G e (3 0 n m )/V (2 0 n m )/P y (1 5 n m ) 

-3 0 -2 0 -1 0 0 1 0 2 0 3 0 

H (O e ) 

Fig. 55: Hysteresis loop of (a) Co(10 nm)/Cu(25 

nm)/Py(25 nm) and (b) Co2MnGe(30 nm)/V(20 

nm)/Py(15 nm) sample, measured by SQUID magnetometery.


Results of the TR-XRMS measurements 

of magnetization dynamics of Py layer in 

Co2MnGe/V/Py system for P (closed blue circles) 

and AP (open black circles) directions of 

Py magnetic moment in respect to the initial direction 

of magnetization in Co2MnGe layer are 

presented in Fig. 56 (a). From the fit of these 

curves, measured at HB = 11 Oe, we obtain 

the change in Landau-Lifshitz damping parameter 

λ/4π from 208 MHz for the P orientation 

to about 224 MHz for the AP orientation and a 

change of precessional frequencies fp from 0.9 

GHz for P to 0.81 GHz for AP configuration. 

Fig. 56: Comparison of magnetization precessional 

dynamics in Py layer for P (open blue circulus) and AP 

(closed black circulus) state for (a): Co2MnGe/V/Py 

and (b): Co/Cu/Py system. 

We performed the measurements of the time 

delay scans for different amplitudes of HB 

and the obtained values of precessional frequency 

(a) and damping (b) for P (circles) 

and AP (squares) configurations are presented 

in Fig. 57. Interestingly, the precessional frequency 

fp in AP state for all values of HB is 

systematically lower than fp for P configuration. 

This result can be interpreted by DWs 

induced coupling mechanism. In AP state the 

domains in the Co2MnGe layer are structured 

such that the stray fields from DWs are mostly 

aligned opposite to the direction of magnetization 

of Py layer. This leads to a reduction of 

the external field at Py layer and as a result 

the value of precessional frequency decreases 

according to the Kittel equation. The higher 

the amplitude of inhomogeneous stray fields 

-48- 

from DWs in Co2MnGe layer are, the stronger 

should be the change in damping parameter of 

Py layer for P and AP configurations. This is 

what we observe in Fig. 57: at the bias fields 

HB where difference in fp for P and AP state 

is higher, we obtained a larger change in LL 

damping parameter. 

l /4 p (M H z ) f p (G H z ) 

1 ,4 

1 ,2 

1 ,0 

0 ,8 

0 ,6 

3 0 0 

2 5 0 

2 0 0 

1 5 0 

(a ) 

(b ) 

6 8 1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 6 2 8 

H B (O e ) 

P 

A P 

P 

A P 

Fig. 57: Values of precessional frequency fp(a) and 

damping parameter λ/4π (b) at P (circles) and AP 

(squares) state in Co2MnGe(30 nm)/V(20 nm)/Py(15 

nm) samples for different values of bias field HB. 

In conclusion, we would like to stress that the 

behavior of the precessional frequency fp when 

changing the mutual orientation of magnetizations 

of two F layers determines the mechanism 

of their coupling. If precessional frequency 

remains identical for both states as for 

Co/Cu/Ni81Fe19 system (Fig. 56 (b)) then configurational 

properties of the spin pumping coupling 

is important; if it changes, then DWs induced 

coupling effect dominates. 

We kindly acknowledge Sabine Erdt-Böhm for 

samples preparation. This work is supported 

by BMBF 05K10PC1. We are also thankful to 

the Helmholtz Zentrum Berlin for travel support 

under BMBF 05 ES3XBA/5. 

References 

[1] L. Thomas, et al. Phys. Rev. Lett 84, 1816 (2000). 

[2] J. Kurde, et. al. New Journal of Physics 13, 

033015 (2011). 

[3] U. Geiersbach, et. al. J. Magn. Magn. Mater 240, 

546 (2002).

Ferromagnetic resonance in the Co/Cu/Py system 


R. Salikhov 1 , A. A. Kamashev 3 , N. N. Garifyanov 3 , F. Radu 2 , I. A. Garifullin 3 and H. Zabel 1 




Conventional ferromagnetic resonance technique at X-band frequency has been 

used for the study of Co/Cu/Py trilayers. Indication for the exchange of spin 

currents pumped from the precessing magnetization of each layer has been found. 

Recently the Co/Cu/Py (where Py=Ni0.81Fe0.19) 

trilayers have been studied using time-resolved 

x-ray resonant magnetic scattering (TR 

XRMS) at the synchrotron facility BESSY II 

[1]. It was found that the magnetic moment of 

iron in permalloy layers exhibits a noticeable 

increase in Landau-Lifshitz (LL) damping parameter 

when changing the mutual orientation 

of magnetizations of Co and Py layers from 

parallel (P) to antiparallel (AP) orientation. 

It was concluded that the increase of damping 

in Py for AP orientation of Co and Py 

magnetic layers in comparison with P orientation 

is associated with the properties of the 

spin-pumping-induced damping. 

Here we have studied Co/Cu/Py spin valve 

system with different thicknesses of ferromagnetic 

Py dP y and Cu dCu spacer layers using a 

conventional ferromagnetic resonance (FMR) 

technique at the frequency 9.3 GHz and in the 

temperature range from 15 to 300 K. We measured 

two series of samples: series I are just the 

samples Co(150 ˚ A)/Cu/Py which were already 

used in TR XRMS [1], series II are the samples 

CoO(200 ˚ A)/Co(30 ˚ A)/Cu/Py in which the 

magnetization of the Co layer is pinned by the 

cobalt oxide bias layer. In series II dCu=30, 

150, 400 ˚ A and dP y=50 and 100 ˚ A 

For the series I we observed two resonance lines 

at room temperature: the first one was observed 

at the resonance field H 1 res � 600 Oe and 

the second one at H 2 res � 1270 Oe. Our analysis 

shows that the first line can be attributed to 

the Co layer and another one - to the Py layer. 

With decreasing the temperature the gap between 

these lines decreased from 740 Oe at 300 

K down to 600 Oe at 20 K. Such a behavior of 

-49- 

the resonance lines may probably indicate that 

coupling of the Co and Py layers occurs due to 

the spin pumping. It is necessary to note that 

in course of these measurements the magnetizations 

of Co and Py layers were always aligned 

(see Fig. 53 (g) of Ref. [1]). 

More interesting behavior demonstrated the 

samples from series II with a CoOx bias layer. 

We have used two regimes of the measurements 

for these samples. In both cases we cooled the 

samples down to about 15 K in an external 

field of 4 kOe. In the first regime we performed 

the FMR measurements with increasing temperature 

(P case). In the second regime after 

cooling, the sample was rotated by 180 o at 

zero magnetic field and measured again with 

increasing temperature (AP case). In both 

regimes we observed a single resonance line 

which may be attributed to the FMR line of 

the ”free” Py layer. For this series of samples 

the Co layer is thinner than in series I. In addition 

to that it is in contact with an antiferromagnetic 

CoO layer which broadens the 

FMR line from the Co layer. Both reasons 

can make the FMR line from the Co layer to 

be invisible. With decreasing temperature the 

FMR line from the Py layer strongly moves to 

lower fields accompanied by a strong broadening. 

Both parameters (resonance field Hres(T ) 

and linewidth ∆H(T )) appear to follow an universal 

curve for all samples (see, e.g., Fig. 58). 

SQUID magnetization measurements show 

that in the first regime of measurements the 

magnetization of the Co and Py layers are parallel 

at all temperatures. At the same time 

at the second regime their magnetizations are 

antiparallel up to 150 K.


(O e ) 

r e s 

H 

D H (O e ) 

1 2 0 0 

1 0 0 0 

8 0 0 

6 0 0 

2 5 0 

2 0 0 

1 5 0 

1 0 0 

5 0 

P 

A P 

(a ) 

P 

A P 

(b ) 

0 

0 1 0 0 2 0 0 3 0 0 

T (K ) 

Fig. 58: Temperature dependence of the resonance 

field (a) and linewidth (b) for P and AP orientation 

of magnetizations in the sample CoO/Co(30 ˚ A)/Cu(150 

˚A)/Py(50 ˚ A). 

(O e ) 

r e s 

H 

D H (O e ) 

1 1 0 0 

1 0 0 0 

9 0 0 

8 0 0 

7 0 0 

2 5 0 

2 0 0 

1 5 0 

1 0 0 

5 0 

d P y = 5 0 A 

d P y = 1 0 0 A 

0 

0 2 0 4 0 6 0 8 0 1 0 0 

T (K ) 

d P y = 5 0 A 

d P y = 1 0 0 A 

(a ) 

Fig. 59: Temperature dependence of the resonance 

field (a) and linewidth (b) for P orientation of 

magnetizations in the sample CoO/Co(30 ˚ A)/Cu(150 

˚A)/Py(dP y). dP y=50 ˚ A and dP y=100 ˚ A. 

The most interesting result of this study is the 

dependencies of Hres(T ) and ∆H(T ) for parallel 

(Fig. 59) and antiparallel (Fig. 60) orientations 

of magnetizations for the samples with 

different thicknesses of the Py layer. From 

these figures it is clearly seen that for the sample 

with thin Py layer (dP y=50 ˚ 1 1 0 0 

1 0 0 0 

9 0 0 

8 0 0 

7 0 0 

6 0 0 

d = 5 0 A 

P y 

d = 1 0 0 A 

P y 

(a ) 

A) the effect is 

more pronounced for both parameters. Moreover, 

for AP orientation we observe a bigger 

2 5 0 

2 0 0 

1 5 0 

1 0 0 

d = 5 0 A 

P y 

d = 1 0 0 A 

P y 

effect. The latter confirms an increase in LL 

damping parameter observed earlier in XRMS 

experiments with the only difference that in 

FMR this effect is seen only at low tempera- 

5 0 

0 

0 2 0 4 0 6 0 

T (K ) 

8 0 

(b ) 

1 0 0 

tures. 

Fig. 60: The same as in Fig. 2) for AP orientation. 

In general, decrease of the resonance field and larger than the distance between two resonance 

increase of the linewidth for Py layer in such lines, these lines start to move to the center of 

a system with decreasing temperature may indicate 

the importance of the spin pumping ef- 

gravity. In the studied case the ωex value increases 

due to increase of spin diffusion length 

fect. Indeed, when one has bilayers consisting of conduction electrons in the Cu layer with 

of ferromagnetic and normal (N) metal layers decreasing temperature. As it has been shown 

the relaxation rate of the F layer very often is theoretically that such dynamic coupling can 

determined by the the spin current pumping. give rise to an effective damping for the free 

In case of F1/N/F2 trilayer precessing magne- layer which depends on the spin-valve configutization 

of each layer is transported by conducration and is sensitive to the bias field acting 

tion electrons of the N layer. This is an analog 

of the classical problem in electron paramag- 

on the pinned layer [3]. 

netic resonance (EPR) for two magnetic ions 

with different g-values coupled by isotropic ex- 

References 

change interaction (see, e.g., [2]). When the [1] R. I. Salikhov, et al. previous article in this jabi 

exchange frequency ωex which causes the spin 

flip between the spins of these ions becomes 

[2] I. A. Garifullin, et al. Fizika Tverdogo Tela 29, 

2118 (1987). 

[3] J.-V. Kim, C. Chappert J. Magn. Magn. Mater. 

-50- 

286, 56 (2005). 

(O e ) 

r e s 

H 

D H (O e ) 

(b )


AC field stimulated dynamics of magnetization in iron film 

K. Zhernenkov, D. Gorkov, B.P. Toperverg and H. Zabel 


Dynamical response of magnetization in thin iron film on the harmonically modulated 

external field is probed with polarized neutron reflectometry (PNR) within 

the radio frequency (RF) range. It is shown that up to 1 MHz the AC field coherently 

tilts the magnetization from its initial direction determined by DC field. 

The latter directed perpendicular to the AC field is applied to suppress possible 

domain kinetics. It is shown that at lowest frequency of 110 kHz the magnetization 

adiabatically follows the AC field, while the maximum tilt angle of the magnetization 

vector decreases by increasing the frequency. No detectable response on AC 

field was observed above 1 MHz. 

Since many decades response of magnetization 

on alternating in time magnetic field was thoroughly 

studied in different systems, e.g. thin 

continues and laterally patterned films and 

multilayes, applying various experimental techniques 

[1]. They predominantly provide an access 

to frequency dispersion of longitudinal and 

transverse components of the homogeneous linear 

susceptibility, or to time resolved direct 

space images. In contrast, specular PNR can 

measure depth resolved the magnetization profile 

and, in principle, can be used to record 

its time, or frequency dependent response to 

AC fields [2]. Simultaneously recording offspecular 

scattering one can resolve the AC 

field response from lateral structures and hence 

study complex domain kinetics. Here, however, 

we report on AC-PNR test measurements aiming 

to address the most simple, but fundamental 

question on AC field stimulated magnetization 

dynamics. The set of measurements has 

been carried out on a 60 nm thick magnetically 

soft iron film. In order to avoid domain formation 

the sample was kept in the saturating 

DC field HDC = 55 Oe much exceeding coercive 

field Hc = 8 Oe. At the same time the DC field 

was used to guide the neutron polarization directed 

along the Y-axis (see Fig.61). The AC 

field HAC(t) = H0 sin(2πft) with an amplitude 

of H0 = 45 Oe and a frequency 0.11 ≤ f ≤ 

1 MHz was applied collinear with the X-axis, 

i.e. perpendicular to the DC field. One can 

expect that in the quasi-static regime, i.e. at 

slow variation of the AC field, the direction of 

-51- 

the magnetization vector M should follow the 

direction of the field H(t) = HDC + HAC(t) deviating 

from the DC field direction for angles 

−40◦ ≤ γ(t) ≤ 40◦ . 

r 

B⊥ y 

γ 

α i 

Basic Equation for PNR from 

B r 

Pi r 

|| 

ki r 

α f 

Fig. 61: Experimental geometry and schematics of 

magnetization tilt due to HAC 

Consequently, the tilt angle γ(t) of magnetization 

should vary coherently within the same 

”opening” angles, neglecting the influence of 

the anisotropy which does not allow to overcome 

the angle γ = 45 ◦ . The magnetization 

tilt with respect to the polarization direction 

causes two effects in PNR. The first one is that 

magnetization projection Mx = M0 sin γ(t) creates 

spin-flip (SF) reflection, R ± = R ∓ , which 

is proportional to sin 2 γ(t). The second ef- 

x 

k r 

P r 

f 

f 

Q r 

z


fect is related to deviations of the projection 

My = M0 cos γ(t) from saturation value M0. 

As a result each non-spin-flip reflection channels 

R ±± is amended by its counterpart R ∓∓ . 

Reflectivity 

Reflectivity 

1.0 

0.8 

0.6 

0.4 

0.2 

Saturation 

f = 110 kHz 

f = 500 kHz 

Model calculations 

Saturation 

f = 110 kHz 

f = 500 kHz 

R + + - - 

, R 

0.0 

0.003 0.006 0.009 0.012 0.015 0.018 0.021 

Incident angle, rad 

0.35 

0.30 

0.25 

0.20 

0.15 

0.10 

0.05 

H AC = 45 Oe, H DC = 55 Oe 

Saturation 

f = 110 kHz 

f = 500 kHz 

Model Calculations 

Saturation 

f = 110 kHz 

f = 500 kHz 

- + 

R 

0.00 

0.003 0.006 0.009 0.012 0.015 0.018 0.021 

Incident angle, rad 

Fig. 62: Reflectivity curves R + + , R − − (top panel) 

and R − + (bottom panel) together with model calculations 

corresponding to the best fit obtained 

Both effects can be well distinguished in 

Fig.62 representing all four reflectivity channels 

recorded at the frequency f = 110 kHz. 

In contrast, at high frequency, as seen from 

Fig.62(bottom panel), no SF reflection was detected, 

except for a small contribution which 

is solely due to the imperfect initial polarization 

and polarization analysis. Also, R + + and 

R − − show respectively only one of the critical 

edges of the total reflection, e.g. for spin ”up”, 

or ”down” states, as it should be, if magnetization 

is fairly collinear with the polarization 

analysis axis. This means that at high frequencies 

the magnetization is not tilted from the 

DC field direction. Note, that in the present 

experiment the reflected signal was not discriminated 

with respect to time and the curves in 

Fig.62 represent reflectivities averaged over the 

time of observation. However, time resolution 

is not really necessary, if the coherency of the 

magnetization tilt is experimentally confirmed. 

This is done by analyzing the relationship between 

time averaged parameters 〈cos γ(t)〉 and 

〈sin 2 γ(t)〉 extracted from the reflectivity fit 

and plotted in Fig.63 as functions of the frequency 

f. Indeed, in case of a coherent tilt 

〈cos 2 γ〉 = 1 − 〈sin 2 γ〉 = 〈cos γ〉 2 and the dispersion 

∆ = 〈cos 2 γ〉 − 〈cos γ〉 2 = 0, as seen 

in Fig.63. From this figure it can be concluded 

that the AC field induced tilt angle 

monotonously decreases with frequency indicative 

for an increasing retardment of the sample 

magnetization response on AC field. In passing 

we also note that no off-specular scattering 

manifesting presence of domains was detected 

over all frequencies. 

Value 

-52- 

1.0 

0.8 

0.6 

0.4 

0.2 

0.0 

cos γ 

sin 2 γ 

Δ 

Bias field amplitude H = 55 Oe 

dc 

AC field amplitude H = 45 Oe 

ac 

0 200 400 600 800 1000 

Frequency, kHz 

Fig. 63: Frequency dependence of parameters sin 2 γ, 

cos γ and ∆ obtained from fit 

References 

[1] M.R. Fitzsimmons, S.D. Bader, J.A. Borchers, 

G.P. Felcher , Furdyna J K, A. Hoffmann, J.B. 

Kortright, Ivan K. Schuller, T.C. Schulthess, S.K. 

Sinha, M.F. Toney, D. Weller, D. Wolf J. Magn. 

Magn. Mater. 271 103 (2004) 

[2] K. Zhernenkov, S. Klimko, B.P. Toperverg, H. 

Zabel, Journal of Phys., Conference Series 211, 

012016 (2010)


Domain kinetics: 90 degrees domain w 

Domain kinetics in iron film under AC magnetic field 

K. Zhernenkov, D. Gorkov, B.P. Toperverg and H. Zabel 


Polarized neutron reflectometry (PNR) is applied to study re-magnetization domain 

kinetics in thin single crystalline iron film. The experiments were carried 

out applying AC field along one of the easy axis in the presence of low DC field 

directed along the orthogonal easy axis. It is shown that the low frequency AC field 

induces nucleation and propagation of domains with magnetization perpendicular 

to the DC field. These processes are substantially suppressed when the frequencies 

exceed 0.5 MHz and finally terminated at about 1 MHz. 

Considering re-magnetization processes in the 

field collinear with the axis of easiest magnetization 

it is usually assumed that magnetization 

reversal involves nucleation and expansion 

of domains with magnetization along the altered 

external field. The model based on this 

scenario was successfully applied to describe 

our data [1] using AC-PNR [2] from single crystalline 

Fe film subjected to AC and DC magnetic 

fields collinear with one of the Fe easy 

axes. The validity of the model was confirmed 

by the fact that reflected neutrons mainly maintain 

their initial spins state, while very little 

spin-flip (SF) reflection was detected. This 

tiny effect, however, could not be ignored and 

has led us to a decision to examine the role 

of domains with magnetization perpendicular 

to the DC field guiding neutron polarization 

in more detail. Due to the biaxial magnetic 

anisotropy of iron such domains can easily be 

nucleated at a small misalignment between external 

field and one of the crystallographic axis, 

mosaicity, or magnetic inhomogeneities, e.g. at 

the sample edges. In order to highlight the role 

and properties of 90 ◦ domains we have carried 

out a set of measurements with AC magnetic 

field, HAC(t) = H0 sin(2πft), with H0 = 45 Oe, 

applied along the X easy axis, as indicated in 

Fig.64. This axis was set perpendicular to the 

neutron polarization guided in low DC field 

HDC = 12 Oe applied along the Y-axis. The 

strength of DC field HDC = 12 Oe, is just above 

the coercive field Hc = 8 Oe, and was chosen 

so that the angle γH(t) between instant direction 

of field at the sample and the Y-axis was 

oscillating between ±γmax = 75 ◦ . 

scenario for bi-axial anis 

-53- 

Y 

X 

magnetization 

DC field: 

DC+AC field 

AC field 

Fig. 64: Schematic view of two stage re-magnetization 

process via 90 ◦ domain walls propagation 

If at t = 0 the sample is completely magnetized 

along the Y-axis, then perpendicular to 

the DC field domains in the quasi-static regime 

can be nucleated at the moments of time t1 

at which HAC(t1) ≈ Hc. After that quickly 

propagating 90 ◦ DWs should result in the flip 

of the net magnetization close to the X-axis. 

There it may stay until the moment of time 

t2 when in the second quarter of the AC field 

period HAC(t2) ≈ HDC. At this moment nucleation 

and propagation of the opposite set 

of 90 ◦ DWs should restore the initial magnetization 

along the Y-axis. Within the subsequent 

half of the AC field period the magnetization 

will flip in opposite direction and then 

finally restored back again. This scenario was 

experimentally confirmed via analyzing all four, 

two non-spin-flip (NSF), R ± ± , and two spin-


flip, R ± ∓ , PNR curves at low AC frequency 

f = 110 kHz. 

Reflectivity 

Reflectivity 

1.0 

0.8 

0.6 

0.4 

0.2 

0.8 

0.6 

0.4 

0.2 

0.003 0.006 0.009 0.012 0.015 0.018 

Incident angle, radians 

R -+ 

0.003 0.006 0.009 0.012 0.015 0.018 

Incident angle, radians 

Saturation 

f = 700 kHz 

f = 110 kHz R 

f = 110 kHz R 


Saturation 

f = 700 kHz 

f = 110 khz R 

f = 110 kHz R 

R -- 

R ++ 

+ + 

- - 

+ + 

- - 

Saturation 

f = 110 kHz 

f = 700 kHz 


Saturation 

f = 110 kHz 

f = 700 kHz 

Fig. 65: PNR data and the best fit to the model 

The results are depicted in Fig.65, where one 

can admit rather strong SF reflection caused 

by the magnetization component perpendicular 

to the initial polarization vector. At the 

same time the spin splitting between NSF R 

+ + 

and R − − reflectivities is small indicating a 

substantial reduction of the mean magnetization 

averaged over the AC field period. Such 

measurements were repeated for a sequence 

of AC field frequencies up to 1 MHz, where 

SF reflecivity almost vanishes, while NSF reflectivities 

approaches to those in saturation. 

From the fit we determined two essential parameters: 

the values averaged over the period 

〈sin 2 γ(t)〉, and 〈cos γ(t)〉, where γ(t) is the instant 

value of the net magnetization tilt angle. 

From Fig.66 it follows that with increasing frequency 

the mean value of the Y-component 

of the magnetization monotonously increases, 

while mean squared deviations of X-projection 

decrease. This means that DWs cannot exactly 

follow sufficiently fast the variation of the 

external AC field. In Fig.66 one can clearly 

see a crossover to non-adiabatic behavior at 

f = 0.4 MHz. At this frequency the dispersion 

∆ = � 〈cos 2 γ(t)〉 − 〈cos γ(t)〉 2 reaches its 

-54- 

maximum value, while it tends to go to zero at 

high and low frequencies. In the first limit magnetization 

does not deviate from that in saturation 

and 〈cos 2 γ(t)〉 = 〈cos γ(t)〉 2 ≈ 1. In 

the second case 〈cos γ(t)〉 ≈ 0 suggesting that 

magnetization with almost equal probability is 

tilted by ∼ ±90 ◦ with respect to DC field. 

Value 

1.0 

0.8 

0.6 

0.4 

0.2 

0.0 

Bias field H dc = 12 Oe AC field H ac = 45 Oe 

cos γ 

sin 2 γ 

Δ - dispersion 

0 200 400 600 800 1000 

Field frequency, f (kHz) 

Fig. 66: Frequency dependence of parameters 〈sin 2 γ〉, 

〈cos γ〉 and ∆. 

It should also be mentioned that at all frequencies 

the presence of small magnetic domains is 

revealed with off-specular scattering measured 

with full polarization analysis. This is illustrated 

in Fig.67, where SF off specular scattering 

is seen as blobs asymmetrically displayed 

above, or below the corresponding SF specular 

ridges. 

Outgoing angle, mrad 

Outgoing angle, mrad 

20 

15 

10 

5 

0 

20 

15 

10 

5 

R ++ 

- - 

R 

H DC = 12 Oe, f = 700 kHz, H AC = 45 Oe 

5.0E-2 

1.7E-2 

3.3E-3 

6.6E-4 

1.3E-4 

2.6E-5 

5.1E-6 

1.0E-6 

R +- 

R -+ 

0 

0 5 10 15 200 

5 10 15 20 

Incident angle, mrad 

Incident angle, mrad 

5.0E-3 

2.7E-3 

Fig. 67: Scattering intensity maps; SF maps are 

scaled by factor 10 

References 

[1] K. Zhernenkov, S. Klimko, B.P. Toperverg, H. 

Zabel, Journal of Phys., Conference Series 211, 

012016 (2010) 

[2] S. Klimko, K. Zhernenkov, B. P. Toperverg and 

H. Zabel, Rev. Sci. Inst. 81, 103303 (2010) 

1.1E-3 

4.2E-4 

1.6E-4 

6.5E-5 

2.5E-5 

1.0E-5

Instrumentation 

-55- 

Instrumentation


-56-


Vector- and angle-resolved MOKE measurements on Fe/MgO(001) 

as preparatory studies for time-resolved femtosecond laser scanning 

Kerr microscopy 

Min-Sang Lee 1,2 , Hartmut Zabel 1 and Thomas Eimüller 1,3 

1 Junior Research Group Magnetic Microscopy, Ruhr-University of Bochum, Universitätsstr. 150, D-44801 

Bochum, Germany 

2 Institute of Experimental Physics IV, Ruhr-University of Bochum, Universitätsstr. 150, D-44801 Bochum, 

Germany 

3 Hochschule Kempten, University of Applied Sciences, Bahnhofstr. 61, D-87435 Kempten, Germany 

We have performed vector- and angle-resolved MOKE measurements on Fe(5 nm) 

/MgO(001) to obtain quantitative information about its magnetic anisotropy. This 

is a crucial preparatory work for our further studies on optically excited ultrafast 

magnetization dynamics, which are currently being carried out using our femtosecond 

laser scanning Kerr microscope. 

Fig. 68: a) the remanence Mr normalized to the saturation 

value MS vs. the azimuthal rotation angle φ of 

the sample, b) the coercivity Hc vs. φ. 

In our contribution to the last year’s Annual 

Report, we presented modifications and extensions 

to our femtosecond laser scanning 

-57- 

Kerr microscope. This setup is currently being 

used to perform spatio-temporally resolved 

studies of optically excited ultrafast magnetization 

dynamics in Fe(5 nm)/MgO(001). Particular 

focus is put on the highly energetic 

spin-waves generated by the spatial inhomogeneity 

of strongly focused optical excitation, 

escaping from the excitation center and thus 

causing additional damping to the magnetization 

precession on the ps-timescale. For this 

purpose it is crucial, firstly, to have a sample 

with good structural quality (i.e. homogeneity, 

crystallinity, thermal stability etc.) and, secondly, 

to well characterize its magnetic properties 

(i.e. determining the saturation magnetization 

MS, the orientation and strength of 

anisotropy, the Landé factor etc.). The first 

requirement was fulfilled by ensuring the epitaxial 

growth of an iron film (5 nm thick) on 

a MgO(001) substrate in a UHV-MBE system 

(deposition at 338 K and post-annealing at 

673 K). For the pre-characterization of sample 

prior to the spatio-temporally resolved studies, 

many different methods such as VSM, vectorand 

angle-resolved MOKE hysteresis measurement, 

and time-resolved MOKE measurement 

based on pump-probe technique (also vectorand 

angle-resolved) are applied. 

In this article, we present the results from the 

vector- and angle-resolved MOKE hysteresis 

measurements. Other measurements and analysis 

are currently on-going. Fig. 68 shows how


Fig. 69: a) vector-resolved hysteresis loops measured 

at φ = 338 deg. (cf. Fig. 68), b) the trajectory of the 

magnetization vector � M during the magnetization reversal 

in a), c) the extended view of the hysteresis loops 

from a) in a larger field range of −1200 ∼ 1200 Oe. 

the normalized remanence Mr/MS and the coercivity 

Hc change depending on the direction 

of magnetization reversal. To obtain angleresolved 

MOKE hysteresis loops, the sample 

was azimuthally rotated about its surface normal 

while the field axis stayed constant, parallel 

to the longitudinal axis (i.e. parallel to the 

sample plane and the plane of incidence of the 

laser beam) and the hysteresis loops were measured 

in the longitudinal Kerr geometry. The 

angular dependence of Mr/MS in Fig. 68 a) 

exhibits a perfect fourfold symmetry with the 

periodicity of 90 deg. suggesting its origin in 

the crystalline cubic anisotropy (CA). This has 

been expected since Fe grows on a MgO(001) 

substrate into a bcc structure along the (001)axis, 

which we also confirmed by X-ray diffractometry. 

However, Hc in Fig. 68 b) shows that 

there is an additional uniaxial anisotropy (UA) 

where the easy axis of this uniaxial anisotropy 

lies parallel to one of the two easy axes of the 

CA. This makes the magnetization along the 

one easy axis less easy than along the other, 

thus we refer to it as “less easy axis”. The 

presence of such additional anisotropy in Fe 

films directly grown on MgO(001) can be attributed 

to the strain across Fe/MgO interface 

caused by the lattice parameter mismatch between 

Fe and MgO. Considering the fact that 

this UA does not influence the angular dependence 

of Mr/MS visibly, as shown in Fig. 68 a), 

and that Hc varies within a very small field 

range (2 ∼ 6 Oe), one can expect the UA to 

be much weaker than the CA in its strength. 

This expectation was also confirmed when we 

estimated the values of the anisotropy constants 

K (2) 

u , K (4) 

u (the anisotropy constants of 

the UA with the first two lowest orders) and 

K (4) 

cubic (the anisotropy constants of the CA with 

the lowest order). The UA turned out to 

be weaker by two orders of magnitude than 

the CA (K (2) 

u /MS ∼ 1 Oe; K (4) 

u /MS ∼ 1 Oe; 

K (4) 

cubic /MS ∼ 100 Oe). This estimation was 

based on the calculation of the integrals of 

magnetization curves (virgin curves) measured 

along the easy, the less easy, and the hard axes. 

-58- 

Fig. 69 demonstrates the capability of our 

setup to perform vector MOKE measurements. 

By measuring the hysteresis loops of the longitudinal 

magnetization component Mx and of 

the transversal magnetization component My, 

the full trajectory of � M during the magnetization 

reversal can be determined. Note that 

the abrupt changes of magnetization shown in 

Fig. 69 a) correspond to the paths along which 

the length of � M is reduced, indicating that the 

reversal of � M along these paths is dominated 

by domain wall motion. The plateaus of the 

steps in Fig. 69 a) are caused by the temporary 

pinning of � M along the less easy axis where the 

length of � M is restored as shown in Fig. 69 b). 

The arm-shaped paths on the far right and far 

left ends in Fig. 69 b) correspond to the large 

field region in Fig. 69 c). Here, the length of 

�M is conserved, meaning that the dominant 

process here is coherent dipole rotation. 

Vector MOKE technique will also be implemented 

in the currently running time-resolved 

MOKE measurements, which will allow us to 

obtain the full 3D precessional trajectory of � M.

Design and results of the new Nano-MOKE setup 

F. Brüssing, M. Stadlbauer, M. Schlottke, G. Badini Confalonieri, H. Zabel 


The magnetic reversal at the nanoscale is in focus of many potential technical applications. 

Here, we present a new instrument aiming at the investigation of the local 

reversal of magnetic nanostructures. The setup is based on the longitudinal Magneto 

Optical Kerr Effect and is ideally suited to measure the magnetic properties 

of thin magnetic films and magnetic nanostructures with in-plane magnetization. 

Fig. 70: The nano-MOKE setup placed on a damped 

optical table and with open shielding 

Highly sensitive local magneto optical measurements 

require stable and well reproducible conditions. 

The environmental conditions during 

a measurement are kept constant due to the 

air-conditioning of the room, a self-leveling active 

isolated optical breadboard of the company 

Thorlabs and a shielding of the entire 

setting via a home made close frame, shown 

in fig. 70. 

However, in addition to the stability conditions 

during the measurements, also the measurement 

itself has to be performed with high precision. 

For this purpose we used a fiber coupled 

diode laser with a wavelength of 635 nm and 

a maximum intensity of 3.5 mW in cw-mode 

(Thorlabs S1FC635) as light source. The spatial 

resolution of approximately 1µm is reached 

due to a collimator (Thorlabs F230FC-B) and 

a beam expander (Thorlabs BE05M-B) which 

generates a wide, parallel broad beam which afterwards 

is polarized for the measurement technique, 

and focused down by an aspheric lens 

onto the sample with focal distance of 20 mm 

and a numerical aperture of 0,534 (Thorlabs 

-59- 

Fig. 71: Top view of the Nano-MOKE setup 

AL2520-A), see fig. 71. 

The magnetic measurement is performed via 

the longitudinal MOKE-effect which results 

from tilting the polarization of the incident 

light due to the magnetization of the sample. 

This rotation is very sensitively detected by the 

use of a lock-in technique in combination with 

a Faraday modulation of the reflected light and 

a polarization analysis. Both prisms for polarization 

and analysis (Rochon-Prisma) are motorized 

in order to guarantee the required accuracy 

for alignment of the components (Newport 

AG-PR100) with an accuracy of 0.002 ◦ 

which suppress additional contributions to the 

longitudinal signal. (fig. 71). 

The magnetic state of the sample is varied via 

a dipole magnet which can apply up to 200mT. 

The design of this magnet opens the possibility 

to put lenses close to the sample surface. This 

magnet and the sample holder are mounted on 

a ground plate which allows to vary the angle 

of incident of the beam.


Fig. 72: Positioning error 

of the sample stage 

Fig. 73: Size of the spot 

in relation to the lens position 

For the movement of the lens system and 

the sample motorized translation stages are 

used (Thorlabs PT3-Z8) with a precision of 

< 0, 2µm. To determine the precision of the positioning 

system one of the motors was moved 

and afterwards the measured position was compared 

with the aimed position, see fig. 72. The 

motorized lens system is necessary to align the 

sample in the focus of the beam with a precission 

of ≈ 1µm. For this reason the reflected 

intensity around an edge of a nano-structure 

is scanned and due to changes of the optical 

parameters the intensity changes at the edge. 

This effected is used to focus the beam. The 

resulting slope in a scan is proportional to the 

spot size. A set of measurements provides the 

possibility to find the best focus which is related 

to the biggest slop, see fig. 73. After alignment 

of the lens the setting can be used for the 

investigation of samples. In figure 74 a comparison 

between an intensity map of the nano- 

MOKE setting and a scanning electron microscope 

(SEM) image of the sample is shown, 

which proves that the setting is suited for measurements 

of nano-structured samples. 

Fig. 74: Comparision of an intensity map measured 

with the nano-MOKE (a) and a SEM image (b) 

-60- 

Additional to the linear movement of the sample 

a rotation of the sample with a accuracy of 

0, 05 ◦ is possible with a rotation stage (Thorlabs 

CR1/M-Z7E). In figure 75 this stage is 

used to investigate an epitaxial Fe-layer (right) 

and Fe-lattice (left) along two different axis. 

For the homogeneous layer the difference between 

the easy axis and the hard axis is easy to 

see. In case of the pattern the shape anisotropy 

and the interaction of the elements changes the 

shape of the hysteresis. 

Fig. 75: MOKE measurement along two different directions 

The setting is also capable of magneto resistivity 

measurements, which allows to compare 

directly the local magnetization to the 

global properties of the magneto resistivity, see 

fig. 76. 

Fig. 76: Right:Image of the sample holder, left: Simultan 

measurment of magnetoresistivity (top) and 

MOKE (buttom) 

We gratefully acknowledge financial support by 

the DFG through SFB491 and the Research 

Department IS3/HTM. Furthermore we would 

like to thank the workshop of the Physics Faculty, 

Jürgen Podschwadek and Jörg Meermann 

for the assistant during construction of the setting 

and Oleg Petracic for the information to 

the basic construction of such a setting.

Lithography Chamber 

D. Demirbas, M. Ewerlin, A. Ludwig, J. Meermann, and O. Petracic 



We report on the design and construction of a new high vacuum chamber, the 

so called ’lithography chamber’ which was built at the institute of experimental 

physics at the RUB. The chamber includes an electron beam evaporator for sample 

preparation as well as an Ar ion gun for etching. 

Nowadays many techniques such as molecular 

beam epitaxy (MBE), ion sputtering, arc evaporation 

and pulsed laser deposition are used for 

the preparation of thin films and multilayers. 

We built up a new chamber in which electron 

beam evaporation technology is used for sample 

preparation. 

Fig. 77: Photo of the ’lithography chamber’. 

Figure 77 shows a photo of the chamber. In 

figure 78 a technical drawing of the chamber is 

depicted. 

The chamber consists of two parts, mainly the 

loadlock and the main chamber. The loadlock 

is used for transfer-in and out of the samples. 

Also heating of the samples up to 500 ◦ C is 

possible. The sample holder can be transfered 

into the main chamber using a transfer rod. In 

the main chamber evaporation as well as etching 

is possible. Depending on the process, the 

sample holder is rotated into the appropriate 

position using the sample-manipulator. The 

films are grown using electron beam evaporation, 

which is a thermal evaporation process 

that requires ultra-high vacuum conditions in 

order to avoid contamination of the evaporated 

-61- 

material by residual gas atoms. Therefore we 

work with a base pressure in the order of 10 −9 

mbar. The evaporation material placed in a 

crucible is hit by a high energy electron beam, 

localy melted and vaporized. The advantage 

of this method is that due to the high energy 

of the electrons high melting temperatures can 

be reached. Therefore this method can be used 

for the evaporation of nearly all materials. 

Fig. 78: Technical drawing of the ’lithography chamber’. 

Fig. 79: X-ray reflectivity of a Co film deposited in 

the ’lithography chamber’.


In our chamber it is possible to place four different 

materials into the e-beam evaporator. The 

evaporation rate is controlled using a quartz 

crystal. This allows a very precise determination 

of the grown film thickness after calibration 

for the used material. Figure 79 shows 

the X-ray reflectivity of a Co film deposited in 

the chamber. The graph shows oscillations up 

to 8.5 ◦ indicating a good quality of the film. 

Fig. 80: Etching holder in etching process. 

The etching is performed using Ar ion milling. 

The ion beam is directed orthogonally onto the 

sample on the substrate holder. To prevent 

back-sputtering into the ion gun a special etching 

holder was constructed. A photo of this 

holder is shown in figure 80. The technical 

drawing is shown in figure 81. The substrate 

is placed on a wedge at an angle of 45 ◦ . 

The etching process in the lithography chamber 

is comparable to the etching process in the 

ion beam sputter chamber. The etching uniformity 

is even improved (see figure 82) so that 

larger areas can be etched. Figure 82 shows the 

etching profile obtained from an array of lithographically 

patterned crosses in a Si-substrate. 

One finds a good uniformity with less than 20% 

List of equipment: 

• Four-pocket e-beam evaporator: EBVM200 (Dr. Eberl) 

• Ar ion gun (Roth & Rau) with plasma bridge neutralizer 

• Ar gas mass flow controller (MKS) 

• Quartz crystall (Hositrad) with thickness monitor (Inficon) 

-62- 

deviation in the etch depth over an area of 12× 

12 mm 2 . 

In the lithography chamber everything is controlled 

manually. During the etching process 

the pressure in the chamber rises to 10 −3 mbar. 

To prevent heating of the samples during the 

etching process, the etching holder can be 

cooled with either water or liquid nitrogen. It 

is possible to perform uniform etching. The 

etching rates are also comparable to the etching 

rates in the sputtering system. 

Fig. 81: Technical drawing of the etching holder. 

Fig. 82: Etching profile of a Si layer etched in the 

chamber. 

Thanks are due to SFB491 for funding.

SuperADAM: recent developments. 

A. Devishvili 1 , A. Dennison 2 , K. Zhernenkov 1 , B. Toperverg 1 and H. Zabel 1 

1 Ruhr-Universität Bochum, 44780 Bochum, Germany 

2 DPMS, Uppsala University, BP 530, 751 21 Uppsala, Sweden 


Within the framework of the millennium program M1 at the ILL and BMBF project 

05KN7PC1 the polarized neutron reflectometer ADAM has been upgraded. The 

new reflectometer has been in regular user operation since 2010. During 2011 the 

reflectometer received upgraded polarizer for off-specular polarization analysis, as 

well as a new goniometer head and translation stages. A minor software improvements 

now provide a full automation of AC-PNR setup and integration of several 

new devices over a serial interface. 

Polarizer / Wavelenght 

filter 

Berillium filter 

Fig. 83: The principle schematics of the polarized neutron reflectometer SuperADAM. 

During the year 2011 the high flux ILL reactor 

has been running for 195 days. Twentyfive 

different experiments were performed on Super- 

ADAM, nine of which were available through 

ILL’s part of the beamtime. 

The instrument consists of two monochromators 

delivering two neutron beams at different 

angles which cross at a pivot point located 

outside of the casemate. In order to provide 

fast switching time between different operation 

modes, the instrument can freely rotate around 

the pivot point. The detector arm can rotate 

around the sample position providing the required 

momentum transfer. The layout of the 

new instrument is depicted on Fig. 83. 

-63- 

New heavy duty goniometer head was installed 

on the sample position. Loads up to 300 kg 

permit installation of any standard sample environment 

on a sample position without any additional 

support equipment. New heavy duty 

translation stages were installed in the detector 

tank. Various heavy polarization and neutron 

detection devices can be manipulated with minimal 

user intervention. 

The new multi-mirror analyzer has been installed 

and tested. The device provides a high 

polarization of up to 98.6% combined with an 

excellent transmission of 76% in a wide angular 

range. The constant nature of neutron polarization 

process removes any complications 

in the data analysis commonly associated with


time dependent 3 He polarization decay in 3 He 

spin filter devices which are mostly used for 

this type of experimental tasks. The example 

of full polarization analysis of off-specular scattering 

of thin iron film is presented in Fig 84. 

Fig. 84: Logarithm of NSF (top panels) and SF (bottom 

panels) of neutron intensity distributed over angles 

of incidence onto and scattering from 100 nm thick Fe 

film subjected to AC magnetic field applied perpendicular 

to DC field guiding neutron polarization. 

In all four maps one can see specular reflection 

ridges running along the main diagonal. 

In the upper panels these ridges represent non 

spin-flip reflectivities of nearly equal intensity, 

suggesting almost equally populated domain 

states with magnetization projection along and 

opposite to the field guiding neutron polarization. 

Intensities of spin flip ridges of specular 

reflectivities in the bottom panels are substantially 

suppressed, but not down to zero suggesting 

a presence of domains with magnetization 

-64- 

perpendicular[1] to the external DC field and 

collinear with AC field. The asymmetry in the 

intensity distribution in the spin-flip maps is 

mostly due to the birefringence [1] of neutron 

waves in the mean optical potential averaged 

over the coherence length, as well as over the 

AC field period. Due to very low intensity of 

this asymmetry in the spin-flip channel it can 

only be observed using the multi-mirror analyzer. 

The AC-PNR option used in those measurements 

have received an upgrade in the principal 

control system. The operation of the AC 

and DC fields components can be performed 

from the instrument control software. The details 

of the AC-PNR setup can be found in [2]. 

The support for several sample environments 

from ILL have been implemented in the instrument 

control software. This upgrade permits 

users to control HPLC pumps, water bath controllers, 

RT100 temperature probes and other 

serial bus devices available on the instrument. 

We gratefully acknowledge financial support 

by the BMBF projects 05KN7PC1 and 

05K10PC1 (since July 1, 2010). 

References 

[1] H. Zabel, K. Theis-Bröhl, B.P. Toperverg, 

in Handbook of Magnetism and Advanced 

Magnetic Materials Vol.12, edited by H. 

Kronmüller and S. Parkin (Wiley, New 

York, 2007), 1237. 

[2] K. Zhernenkov, S. Klimko, B.P. Toperverg, 

H. Zabel, Journ. of Physics: Conf. 

Series 211 (2010) 012016


Imaging with Low Temperature Magnetic Force Microscope 

G. A. Badini Confalonieri 1 , K. Gross 1 , and H. Zabel 1 

Institut für Experimentalphysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany 

In this report we detail the procedure used to perform low temperature magnetic 

force microscopy measurements with the HV Solver (NT-MDT) instrument available 

at EP IV. A microstructured Heusler alloy, of known room temperature magnetic 

behavior, was used as test sample. 

The HV Solver (NT-MDT) Atomic and Magnetic 

force microscope (AFM /MFM) available 

at EP IV is capable of RT atomic and magnetic 

force microscopy measurements (AFM/MFM) 

with the possibility to apply variable magnetic 

field parallel to the sample stage surface. 

An additional piezo-step motor control stage 

can be used in order to perform angle dependent 

measurements. The AMF/MFM is placed 

inside a vacuum chamber and connected, by a 

transference line, to a N2 dewar in order to allow 

temperature dependent measurements. In 

the following sections, a list of guidelines for 

the correct use of the AFM/MFM microscope 

in low temperature mode will be presented. 

Fig. 85: (a) the reduction of the applied field from 

the nominal value when using the rotating sample stage 

and (b) in plane field gradient between the magnetic 

poles at a nominal maximum value of applied field of 

1000 Oe. 

The magnetic tip used during measurements 

utlimately plays a major for the quality of 

the magnetic contrast. Two commercial tips 

have been tested at RT: Multi75M-G and PPP- 

MFMR. Their difference lays mainly on the 

quality of the magnetic coating which ultimately, 

determines the quality of the magnetic 

contrast. the tip from PPP-MFMR, showed 

a somewhat higher resolution and was finally 

chosen for the temperature measurements. 

Usually, the sample is mounted on a 10 mm 

high copper cylinder. An optional rotating 

-65- 

stage can also be used in order to perform angle 

dependent measurements. However, care 

must be taken when applying a magnetic field. 

In fact, the profile of the rotating stage rises 

approximately 2 mm above the top edge of the 

magnetic poles between which it sits. The magnetic 

field experienced by the sample is therefore 

different from the nominal field, as shown 

in Fig. 85(a). 

With the use of the rotating stage, vertical component 

of the field should also be expected. For 

the purpose of low temperature measurements 

it is advisable to use, whenever possible, the 

traditional copper stage which, being made of 

a single copper piece, has also the advantage 

of ensuring good thermal conductivity between 

the sample and the nitrogen cold finger. 

As a final remark, the user should be aware of 

the presence of an in-plane field gradient between 

the magnetic poles (separated by a gap 

of approx 25mm), which becomes particularly 

relevant when working with large area samples. 

As an example, the field gradient measured 

when the maximum field is applied, and the 

sample is mounted on the single copper support, 

is shown in Fig. 85(b). Clearly, at the 

centre of the stage, the sample experience a 

magnetic field that is approximately fifty percent 

of the nominal value of 1000 Oe.


Fig. 86: Room temperature MFM imagine of a 

Heusler alloy using (a) Multi75M-G tip and (b) PPP- 

MFMR tip. (c) The same image taken at 153K, showing 

a much deteriorated contrast. 

For low temperature measurements, high vacuum 

should be established in the chamber before 

starting the cooling process. Using the N2 

cold trap it is possible to achieve 5E-8 mbar 

pressure. A vacuum of 1E-7 mbar or less is 

acceptable to start the cooling sequence. For 

technical details on the vaccum and cooling 

procedure, the reader is remitted to the instruction 

guide prepared by Dr. A. Schumann. It 

should be remembered that the spring constant 

of the tip is pressure dependent. However it 

saturates at approx 10 −3 mbar. 

Lowering the pressure further brings forth no 

change on its mechanical properties. Timewise, 

at the moment of planning a measurement, 

it should be noted that a complete vacuum 

process requires an overnight pumping of 

the chamber. When cold nitrogen gas is flown 

within the AFM/MFM stage, the temperature 

start decreasing and the final temperature will 

depend on the pressure within the N2 dewar, 

which, in turn, determines the cold gas flow 

rate. Care should be taken not to rise the pressure 

to the point that liquid N2 start entering 

the cooling system. If that will happen a considerable 

amount of noise will appear during 

the measurements. 

-66- 

For the test measurement, T was fixed at 153 

K. A stability of 1 K can be achieved over 

the course of several minutes, allowing imaging 

at constant T. Test measurements, shown 

in Fig. 86, clearly show that the quality of the 

MFM contrast at low T worsened with respect 

to the RT contrast. This can be explained by 

the change in elastic constant of the tip in vacuum, 

as mentioned above, which results in a 

change in the mechanical oscillation of the cantilever. 

A useful figure of merit to predict the performance 

of the tip in high vaccum is the mechanical 

quality factor at resonance, Q. In the tip 

used in this work, the low value of Q resulted 

in loss of tip stabilty during scanning. This 

created a series of artefacts in the image, in 

the form of periodic contrast oscillations, as 

they can be observed in Figure 2c. To overcome 

this problem a high Q factor tip should 

be used, bearing in mind tht the higher Q, the 

stiffer the tip and, therefore, the lower the resolution. 

As a final precaution, particularly when attempting 

temperature measurements on metallic 

sample, care should be taken not to confuse 

electrostatic contrast on the sample surface 

for magnetic contrast. It is good practice 

to ground the sample by connecting it, electrically, 

with the sample holder. A more detailed 

explanation on how to deal with electrostatic 

contrast can be found in [1]. 

The authors wish to acknowledge the financial 

support of the SFB 491 project. 

References 

[1] M. Jaafar, O. Iglesias-Freire, L. Serrano-Ramon, 

M. Ricardo Ibarra, J. M. de Teresa and A. Asenjo, 

Beilstein J. Nanotech. 2, 552 (2011)

Part II 

Publications and Conference 

Contributions 

Published in 2011 

PUBLICATIONS - CONFERENCES 

Structural and magnetic characterization of self-assembled iron oxide nanoparticle 

arrays 

M. J. Benitez, D. Mishra, P. Szary, G. A. Badini Confalonieri, M. Feyen, A. H. Lu, L. Agudo, 

G. Eggeler, O. Petracic, and H. Zabel, J. Phys.: Condens. Matter. 23, 126003 (2011). 

Fingerprinting the magnetic behavior of antiferromagnetic nanostructures using 

remanent magnetization curves 

M. J. Benitez, O. Petracic, H. Tüysüz, F. Schüth, and H. Zabel, Phys. Rev. B 83, 134424 

(2011). 

Template-assisted self-assembly of individual and clusters of magnetic nanoparticles 

G. A. Badini Confalonieri, V. Vega, A. Ebbing, D. Mishra, P. Szary, V. M. Prida, O. Petracic, 

and H. Zabel, Nanotechnology 22, 285608 (2011). 

Tuning the magnetic properties of Co nanoparticles by Pt capping 

A. Ebbing, O. Hellwig, L. Agudo, G. Eggeler, and O. Petracic, Phys. Rev. B 84, 012405 (2011). 

Magnetotransport properties of Cu2MnAl, Co2MnGe and Co2MnSi -Heusler alloy 

thin films: from the nanocrystalline, disordered state to the long range ordered 

crystalline state 

M. Obaida, K. Westerholt and H. Zabel, Phys. Rev. B 84, 184416 (2011). 

Adaption of a diffractometer for time-resolved X-ray resonant magnetic scattering 

S. Buschhorn, F. A. Brüssing, R. Abrudan, and H. Zabel, J. Synchrotron Rad. 18, 212 (2011). 

Depletion at Solid-Liquid Interfaces: Flowing Hexadecane on Functionalized Surfaces 

P. Gutfreund, M. Wolff, M. Maccarini, S. Gerth, J. F. Ankner, J. Browning, C. E. Halbert, H. 

Wacklin, and H. Zabel, J. Phys. Chem. 134, 064711 (2011). 

Magnetic domain fluctuations in an antiferromagnetic film observed with coherent 

resonant soft x-ray scattering 

S. Konings, C. Schüßler-Langeheine, H. Ott, E. Weschke, E. Schierle, H. Zabel, and J. B. 

Goedkoop, Phys. Rev. Lett. 106, 077402 (2011). 

Precessional damping of Fe magnetic moments in a FeNi film 

S. Buschhorn, F. Brüssing, R. Abrudan, and H. Zabel, J. Phys. D: Applied Physics, 44, 165001 

(2011). 

Nanoscale Discontinuities at the Boundary of Flowing Liquids: A Look into Structure 

-67-


M. Wolff, P. Gutfreund, A. Rühm, B. Akgun and H. Zabel, J. Phys.: Condensed Matter 23, 

184102 (2011). 

Development of magnetic moments in Fe1−xNix - alloys 

B. Glaubitz, S. Buschhorn, F. Brüssing, R. Abrudan, H. Zabel, J. Phys.: Condensed Matter 

23, 254210 (2011). 

Interpretation of small-angle diffraction experiments on opal-like photonic crystals 

F. Marlow, M. Muldarisnur, P. Sharifi, and H. Zabel, Phys. Rev. B 84, 073401 (2011). 

Magnetic domain patterns in Co2MnGe -Heusler nanostripes K. Gross, P. Szary, O. Petracic, 

F. Brüssing, K. Westerholt, and H. Zabel, Phys. Rev. B 84, 054456 (2001). 

Precessional dynamics and damping in Co/Cu/Py spin valves 

R. Salikhov, R. Abrudan, F. Brüssing, St. Buschhorn, M. Ewerlin, D. Mishra, F. Radu, I. A. 

Garifullin, and H. Zabel, Appl. Phys. Lett. 99, 092509 (2011). 

Self organization of magnetic nanoparticles: A polarized grazing incidence small 

angle neutron scattering and grazing incidence small angle x-ray scattering study 

K. Theis-Bröhl, D. Mishra, B. P. Toperverg, H. Zabel, B. Vogel, A. Regtmeier, and A. Hütten, 

J. Appl. Phys. 110, 102207 (2011). 

Easily made and handled carbon nanocones for scanning tunneling microscopy and 

electroanalysis 

J. Sripirom, S. Noor, U. Köhler, A. Schulte, Carbon 49, 2402 (2011). 

Isolated Silicon Dangling Bonds on a Water-Saturated n+-Doped Si(001)-2x1 Surface: 

An XPS and STM Study 

J.-J. Gallet, F. Bournel, F. Rochet, U Köhler, S. Kubsky, M.G. Silly, F. Sirotti, D. Pierucci, J. 

Phys. Chem. C 115, 7686 (2011). 

Thermal behavior of MOCVD-grown Cu-clusters on ZnO(10-10) 

M. Kroll, T. Löber, V. Schott, C.Wöll, U. Köhler, Phys. Chem. Chem. Phys., 14, 1654 (2011). 

In-plane Correlations in a Polymer-Supported Lipid Membrane Measured by Off- 

Specular Neutron Scattering 

M.S. Jablin, M. Zhernenkov, B.P. Toperverg, M. Dubey, H.L. Smith, A. Vidyasagar, R. Toomey, 

A.J. Hurd, J.Majewski, Phys. Rev. Lett. 106, 138101 (2011). 

Spatial Fluctuations of Loose Spin Coupling in CuMn/Co multilayers 

T. Saerbeck, N. Loh, D. Lott, B.P. Toperverg, A.M. Mulders, A. Fraile Rodríguez , J.W. 

Freeland. Wisniowski, M. Ali, B.J. Hickey, A.P.J. Stampfl, F.Klose, R.L. Stamps, Phys. Rev. 

Lett. 107, 127201 (2011). 

Induced magnetic Cu moments and magnetic ordering in Cu(2)MnAl thin films on 

MgO(0 0 1) observed by XMCD 

B. Krumme, H. Herper, D. Erb, C. Weis, C. Antoniak, A. Warland, K. Westerholt, P. Entel 

and H. Wende , J. Phys. D: Appl. Phys. 44, 415004 (2011). 

Field cooling-induced magnetic anisotropy in exchange biased CoO/Fe bilayer studied 

by ferromagnetic resonance 

A. Numan, K. Sinan, A. Bakir, B. Aktas, M. Ozdemir, H. Inam, M. Obaida, J. Dudek and K. 

Westerholt, J. Magn. Magn. Mater. 323, 346 (2011). 

-68-

Published and to be published in 2012 


Self-assembled iron oxide nanoparticle multilayer: x-ray and polarized neutron 

reflectivity 

D. Mishra , M. J. Benitez, G. A. Badini Confalonieri, P Szary, F. Brüssing, O.Petracic, K. Theis- 

Bröhl , A. Devishvili, A.Vorobiev, O. Konovalov, M. Paulus, Ch. Sternemann, B.P. Toperverg 

and H. Zabel, Nanotechnology 23, 055707 (2012). 

Specular and off-specular polarized neutron reflectometry of canted magnetic domains 

in loose spin coupled CuMn/Co multilayers 

T. Saerbeck, N. Loh, D. Lott, B.P. Toperverg, A. M. Mulders, M. Ali, B. J. Hickey, A. P. J. 

Stampfl, F. Klose, and R. L. Stamps, Phys. Rev. B, 014411 (2012) . 

Conference Contributions 

DPG-Frühjahrstagung Dresden 2011, March 14 - 18, 2011 

G. A. Badini Confalonieri, V. Vega, A. Ebbing, D. Mishra, P. Szary, V. M. Prida, O. Petracic, 

and H. Zabel 

Template assisted self-assembly of individual and clusters of magnetic nanoparticles, Talk 

M. Obaida, K. Westerholt and H. Zabel 

Magnetoresistance and anomalous Hall Effect measurements of Co2MnGe and Cu2MnAl Heusler 

alloy thin film microstructures, Talk 

P. Szary, G. A. Badini Confalonieri, D. Mishra, M. J. Benitez, M. Feyen, A. H. Lu, L. Agudo, 

G. Eggeler, O. Petracic, and H. Zabel 

Magnetic and transport properties of Py/ iron-oxide nanoparticle composite systems, Talk 

M. Lange, P. Szary, F. Brüssing, O. Petracic, and H. Zabel 

An experimental approach to a 2-dimensional random resistor network, Poster 

R. Salikhov, I. Garifullin, N. Garif’yanov, L. Tagirov, K. Westerholt, and H. Zabel 

Experimental observation of the spin screening effect in superconductor/ferromagnet thin film 

heterostructures, Talk 

S. Noor, S. Özkan, and U. Köhler 

Structural and magnetic investigations of Fe3Si/GaAs(001), Talk 

S. Frey, M. Kroll, and U. Köhler 

HR-EELS studies on zinc oxide powders samples, Poster 

C. Godde, U. Köhler 

Magnetic and structural investigations of thin ferromagnetic CrSb layers on GaAs(110)/GaAs(001) 

Talk (C. Godde), Talk 

G. K. Gross, P. Szary, O. Petracic, K. Westerholt, and H. Zabel 

Magnetic domain patterns in Co2MnGe-Heusler nanostripes, Talk 

F. Brüssing, M. Ewerlin, R. Abrudan, and H. Zabel 

Magnetic reversal in a laterally structured spin valve system with one tuneable magnetic layer, 

Talk 

D. Mishra, M. J. Benitez, P. Szary, G. A. Badini Confalonieri, M. Feyen, A. Lu, L. Agudo, G. 

Eggeler, O. Petracic and H. Zabel 

-69-


Structural and magnetic characterization of self-assembled iron oxide nanoparticles, Talk 

M. Ewerlin, D. Demirbas, L. Agudo, G. Eggeler, and O. Petracic 

Shift of the blocking temperature of Co nanoparticles by Cr capping, Poster 

D. Demirbas, M. Ewerlin, F. Brüssing, O. Petracic and H. Zabel 

Magnetization reversal in dipolarly coupled PdFe nanodot arrays, Poster 

Meeting of the DGKK Kinetic Division, Clausthal, Mar. 31 - Apr. 

1, 2011 

S. Noor, S. Özkan, and U. Köhler 

Structural and magnetic investigations of Fe3Si/GaAs(001), Talk 

C. Godde, S. Noor, Atena Rastgoo Lahrood, Christian Urban, U. Köhler 

Investigation of island growth and alloy formation during thermal processing of thin iron layers 

on GaAs, Talk (C. Godde) 

Recent Trends in Nanomagnetism, Spintronics and their Applications, 

Ordizia, June 1 - 4, 2011 



Magnetics and Optics Research International Symposium 2011, Nijmegen, 

The Netherlands, June 21 - 24, 2011 

R. Salikhov, R. Abrudan, F. Brüssing, St. Buschhorn, F. Radu, I. A. Garifullin, and H. Zabel 

Time-resolved XRMS in Co/Cu/Py spin valve system: evidence for spin pumping effects, Talk 

European Conference on Neutron Scattering, Prag, July 18-22, 2011 

Kirill Zhernenkov, Dmitry Gorkov, Boris Toperverg, Hartmut Zabel 

Probing magnetization kinetics by frequency dependent polarized neutron reflectivity, Talk 

A. Devishvili, A. Dennison, K. Zhernenkov, A. Schebetov, V. Syromyatnikov, N. Pleshanov, P. 

Gutfreund, M. Wolff, A. Rennie, B. Hjövarsson, B. Toperverg, H. Zabel 

SuperADAM: the upgraded polarized neutron reflectometer, Poster 

XXII Congress and General Assembly of the International Union of 

Crystallography, Madrid, Spain, Aug. 22 - 29, 2011 

B.P. Toperverg 

Polarized Neutron and Light Scattering from Magnetic Nano-structures under AC-field, Invited 

Talk 

ECOSS 28, Breslau, Sep. 26 - 29, 2011 


-70-


Study of Cu-clusters on single crystalline ZnO with STM-Lithography, Poster 

Concluding Conference of the SFB 491, Bochum, Sept. 26 - 28, 2011 

O. Petracic 

Structural and magnetic properties of nanoparticle superlattices, Talk 



T. Eimüller 

Magnetic imaging with fs-laser pulses and x-rays, Talk 

M.-S. Lee 

Spatio-temporally resolved studies of ultrafast magnetization dynamics, Poster 

H. Zabel 

Lateral Magnetic Nanostructures, Talk 


Garifullin, and H. Zabel 

Time-resolved XRMS in Co/Cu/Py system: precessional dynamics and damping, Poster 

S. Noor, S. Özkan, L. Elbers, N. Melnichak, I. Barsukov, W. Fehl, H. Harutyunyan, A. Ludwig, 

D. Reuter, M. Farle, and U. Köhler 

Structural and magnetic investigations of Fe3Si/GaAs(001) and the fabrication and characterization 

of CEO spin LEDs, Poster 

C. Godde, S. Noor, A. Rastgoo Lahrood, G. Nowak, F. Brüssing, H. Zabel, and U. Köhler 

Magnetic and structural investigations of iron based nanostructures and thin CrSb layers on 

GaAs, Poster (C. Godde) 

G. K. Gross, P. Szary, O. Petracic, F. Brüssing, K. Westerholt, and H. Zabel 

Magnetic domain patterns in Co2MnGe-Heusler nanostripes, Poster 

F. Brüssing, M. Ewerlin, R. Abrudan, and H. Zabel 


Poster 



SFB 558 Workshop, Klaukenhof, Sep. 26-29, 2011 


Combined in-situ HR-EELS and STM/STS measurement, Talk 

GISAXS 2011, Hasylab, Hamburg, October 10 - 12, 2011 

D. Mishra , M. J. Benitez, O. Petracic, G. A. Badini Confalonieri, P. Szary, F. Brüssing, K. 

Theis-Bröhl , A. Devishvili, A. Vorobiev, O. Konovalov, M. Paulus, C. Sternemann, B. P. 

Toperverg and H. Zabel 

-71-


Self-assembled magnetic nanoparticles: x-ray and polarized neutron scattering, Poster 

Science Vision for the European Spallation Source, Bad Reichenhall, 

October 10 - 12, 2011 

H. Zabel 

Nanostructures, Invited talk 

Reflectometry for ESS: demands and perspectives, Bad Reichenhall, 

October 13, 2011 

H. Zabel 

Reflectometry at the ESS - Challenges and Perspectives, Invited Talk 

Emergent magnetic monopoles in frustrated magnetic systems, The 

Kavli Royal Society International Centre, Chicheley Hall, October 17 

- 18, 2011 

A. Schumann, F. Brüssing, P. Szary, H. Zabel 

Magnetic dipole configurations on honeycomb lattices: effect of finite size, boundaries, and 

defects, Invited talk 

Physics at the nanoscale, Madrid, Oct. 18 - 21, 2011 

O. Petracic 

Structural and magnetic properties of nanoparticle superlattices, Talk 

9. Materialwissenschaftlicher Tag, Ruhr-Universität Bochum, Nov. 

15, 2011 



C. Fink, P. Szary, G. A. Badini Confalonieri, D. Mishra, M. J. Benitez, M. Feyen, A. H. Lu, 

L. Agudo, G. Eggeler, and O. Petracic 

Magnetic and transport properties of Py/iron-oxide nanoparticle composite systems, Poster 

S. Noor, S. Özkan, L. Elbers, N. Melnichak, I. Barsukov, W. Fehl, H. Harutyunyan, A. Ludwig, 

D. Reuter, M. Farle, and U. Köhler 

Structural and magnetic investigations of Fe3Si/GaAs(001) and the fabrication and characterization 

of CEO spin LEDs, Poster 


Cluster footprint and EELS studies of zinc oxide, Poster 

C. Godde, S. Noor, A. Rastgoo Lahrood, G. Nowak, F. Brüssing, H. Zabel, and U. Köhler 

Magnetic and structural investigations of iron based nanostructures and thin CrSb layers on 

GaAs 

Poster (C. Godde) 

-72-


D. Mishra , M. J. Benitez, O. Petracic, D. Greving, G. A. Badini Confalonieri, P. Szary, F. 

Brüssing, K. Theis-Bröhl, A. Devishvili, A. Vorobiev, O. Konovalov, M. Paulus, C. Sternemann, 

B. P. Toperverg and H. Zabel 

Self-assembled magnetic nanoparticles: x-ray and polarized neutron scattering, Poster 



Third Joint BER II and BESSY II Users’ Meeting, Berlin, Nov. 30 - 

Dec. 2, 2011 


Garifullin, and H. Zabel 

Time-resolved XRMS in Co/Cu/Py system: precessional dynamics and damping, Poster 

Brüssing, Melanie Ewerlin, Radu Abrudan, and Hartmut Zabel 


Poster 

-73-


-74-

Part III 

LECTURES, TALKS & TEACHING 

Invited Lectures, Talks, and Course 

Teaching 

Invited talks 

Oleg Petracic 

Structural and magnetic properties of nanoparticle superlattices 


Structural and magnetic properties of nanoparticle superlattices 

Physics at the nanoscale, Symposium, Madrid, Oct. 18 - 21, 2011 

Kurt Westerholt 

Ferromagnetic Heusler alloy thin films: Surprises and challenges 


Triplet Superconductivity in Josephson junctions with Heusler barriers 

MMM Conference Scottsdale, USA, Oct. 25 - 30, 2011 

Hartmut Zabel 

Magnetic thin films and superlattices 

21th HERCULES Course, Grenoble, France, March 28, 2011 

Atomkraft, Nein Danke ??? -Von der ersten Kernspaltung zur zivilen Nutzung der 

Kernenergie- 

Zwischen Brötchen und Borussia, Dortmund, May 21, 2011 

Inelastic neutron and x-ray scattering for the investigation of Phonons 

Summerschool SFB 616: ”Exciting excitations: From Methods to Understanding”, Waldbreitbach, 

July 25-29, 2011 

Structure and Magnetism of thin Heusler films 

Seminar, Transregio 80: From electronic correlations to functionality, TU MAünchen, ↩ July 28, 

2011 

Fascinating magnetic properties of Heusler alloys 

Condensed Matter Seminar, Uppsala, Schweden, August 9, 2011 

1. Lecture: Basics of Magnetism: Magnetic response 

2. Lecture: Basics of Magnetism: Paramagnetism 

3. Lecture: Basics of Magnetism: Local Moments 

European School on Magnetism, Bucarest, Romania, August 23-28, 2011 

Nanostructures 

Science Vision for the European Spallation Source, Bad Reichenhall, October 10 - 12, 2011 

-75-


Reflektometry at the ESS ? Challenges and Perspectives, Hard Matter 

Reflectometry for ESS? demands and perspectives, Bad Reichenhall, October 13, 2011 

Magnetic dipole configurations on honeycomb lattices: effect of finite size, boundaries, 

and defects 

Emergent magnetic monopoles in frustrated magnetic systems, The Kavli Royal Society International 

Centre, Chicheley Hall, October 17 - 18, 2011 

Quasikristalle 

Physikalisches Kolloquium, Ruhr-Universität Bochum, November 7, 2011 

-76-

Committee and review panel work 

Hartmut Zabel 


Speaker of the Sonderforschungsbereich (SFB) 491 der DFG: ”Magnetische Heteroschichten: 

Spinstruktur und Spintransport” 

Co-Chief Editor of the Journal ”Superlattices and Microstructures”, Elsevier 

Member of the ”Komittee Forschung mit Neutronen” (KFN) and Spokesperson for neutron 

instrumentation, Spokesperson for ”Instrumentation and Infrastructure” 

Chair of the Scientic Council of the Dynamitron-Tandem Accelerator at the Ruhr-University 

Bochum 

Member of the AG Magnetism, AK Festkörperphysik, Deutsche Physikalische Gesellschaft 

Member of the BESSY Beam Time Committee 

Member of the Selection Panel for the German-Israeli Foundation for Scientific Research and 

Development (GIF) 

Member of the BMBF Evaluation Committee Verbundforschung Erforschung kondensierter Materie 

am Grossgeräten 2007-2010. 

Member of the Selection Committee of the Danish Council for Independent ResearchResearch 

Member of the Swedish Science Foundation Selection Panel Successful Research Leaders 

Member of the DOE Review Panel of the Argonne National Laboratory Materials Science 

Division. 

-77-


-78-

Course teaching 

Wintersemester 2010/2011 

Vorlesung: Einführung in die Festkörperphysik 

Dozent: Prof. Dr. U. Köhler 

Vorlesung: Einführung in die Oberflächenphysik 


Seminar: Präsentation physikalischer Inhalte 


Vorlesung: Physik für Mediziner 

Dozent: Prof. Dr. Dr. H. Zabel 

Vorlesung: Physik I für Biologen 

Dozent: Prof. Dr. K. Westerholt 

Vorlesung: Physik im Reformstudiengang für Mediziner (POL) 


Vorlesung: Nanomagnetism 2 

Dozent: PD Dr. Oleg Petracic 

Sommersemester 2011 

Vorlesung: Einführung in die Festkörperphysik II 




Vorlesung: Magnetism in Condensed Matter 


Vorlesung: Exploring Condensed Matter at Large Scale Facilities 




Vorlesung: Physik II für Biologen 


Vorlesung: Nanomagnetism 


Wintersemester 2011/2012 


Vorlesung: Physik I für Studierende der Biochemie, Chemie und Geowissenschaften 


Vorlesung: Einführung in die Oberflächenphysik 


-79-






Vorlesung: Medizinische Physik: Einführung in die Grundlagen 


Vorlesung: Einführung in die Festkörperphysik I 


Vorlesung: Supraleitung in Festkörpern 


-80-

Guest Lectures 


January 13, 2011 

Prof. Dr. H.-J. Elmers, Universität Mainz 

Interplay of structure, magnetism and electronic states in ferromagnetic half-metal and shape 

memory Heusler alloys 

January 27, 2011 

Dr. Axel Hoffmann, Argonne National Laboratory, USA 

Pure Spin Currents: Discharging Spintronics 

April 14, 2011 

PD Dr. Guido Meier, Institute of Applied Physics, University of Hamburg 

Time Resolved Imaging of Magnetization Dynamics on the Nanoscale 

May 5, 2011 

Prof. Dr.Wolfgang Kuch, Freie Universität Berlin 

Magnetic properties of antiferromagnetic/ferromagnetic thin film systems and paramagnetic 

molecules adsorbed on ferromagnetic thin films 

July 14, 2011 

Prof. Dr. Manfred Albrecht, Universität Chemnitz 

Modern Concepts and materials for magnetic data storage 

August 8, 2011 

Prof. Dr. Joe Trodahl, Victoria University of Wellington, New Zealand 

Rare-Earth Nitrides: Intrinsic Ferromagnetic Semiconductors 

November 17, 2011 

Dr. Florian Kronast, Helmholtz-Zentrum-Berlin 

Imaging magnetic responses of three-dimensional nanomagnets by XPEEM 

November 24, 2011 

Prof. Dr. Peter Böni, TU München 

Chromium: Unraveling its intriguing properties 

December 8, 2011 

Prof. Dr. Gisela Schütz, MPI Stuttgart 

Magnetische Röntgenmikroskopie (Magnetic X-ray Microscopy) 

-81-


-82-

Part IV 

WORKSHOPS and CONFERENCES 

Workshops and Conferences organized 

by the Institute of Experimental 

Physics/Solid State Physics 

Concluding Conference of the SFB 491: Magnetic Heterostructures, 

September 26-29, 2011, Ruhr-University Bochum 

Program Committee: M. Farle, M. Hofmann, J. König, H. Zabel 

Organization Committee: S. Grubba, H. Hantusch, J. Lindner, O. Petracic 

Speakers & Topics 

Tuesday, September 27, 2011 

Opening 

Prof. Dr. E. Weiler, Rektor der Ruhr-Universität Bochum 

Prof. Dr. J. Schröder, Prorektor, Universität Duisburg-Essen 

Prof. Dr. U. Czarnetzki, Dekan, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum 

B. Hillebrands, Magnon Spintronics 

M. Farle, Control of spin dynamics by manipulating relaxation channels of the magnetization 

C.M. Schneider, Perspectives of Immersion Lens Microscopy for Magnetism Studies 

C. Back, Non local magnetization dynamics due to spin pumping 

T. Eimüller, Magnetic imaging with fs-laser pulses and x-rays 

J. Lindner, Microstrip-resonators: An approach to detect single nanostructure Ferromagnetic 

Resonance 

J. Kirschner, High energy surface magnons 

D. Hägele, Detection of incoherent dynamics in magnetic systems 

M. R. Hofmann, Spin controlled optoelectronic devices 

P. Bruno, Exploring the quantum frontier of spin dynamics 

Poster Session 

Wednesday, September 28, 2011 

C. Felser, Rational Design of New materials: from Topological Insulators to Spintronics 

K. Westerholt, Heusler alloys in thin film heterostructures: surprises and challenges 

P. Kratzer, Magnetic thin films on semiconductors or insulators: the role of interface atomic 

structure 

K.-H. Schwarz, DFT electronic structure calculations of solids with WIEN2k 

H. Wende, Magnetic heterostructures studied element specifically: towards a microscopic understanding 

of magnetic interactions 

H. Herper, Hybrid structures with ferromagnetic Heusler compounds: An ab initio investigation 

G. Reiss, A short trip through the life of a magnetic tunnel junction 

W. Kleemann, Multiferroics and Magnetoelectric Materials 

-83-


G. Bacher, Control of spin transport and spin dynamics by external fields 

K. B. Efetov, Odd triplet Superconductivity in Superconductor-Ferromagnet structures 

J. König, Superconducting Proximity Effect in Quantum-Dot Systems 

Banquet in Haus Herbede 

Thursday, September 29, 2011 

P. Ziemann, Size dependent properties of FePt nanoparticles 

U. Köhler, Structure and magnetism of ferromagnetic layers for spin injection on III-V semiconductors 

O. Petracic, Structural and magnetic properties of nanoparticle superlattices 

R. Allenspach, Magnetic domain walls in nanomagnets 

H. Zabel, Lateral magnetic nanostructures 

Closing remarks 

-84-

Weihnachtskolloquium im Haus Herbede 

Bochum, December 21, 2011 

Dr. Till Schmitte (Mannesmann/Salzgitter) 

Visualisierung von Ultraschall mit dem photoelastischen Effekt 

Dr. Dirk Sprungmann (Autohaus Sprungmann) 

Die VW Leo Sprungmann GmbH - Sanierung eines Familienbetriebes 

Dr. Alexandra Brennscheidt (VDI Düsseldorf) 

VDI Technologiezentrum - Forschungsförderung und Innovationsbegleitung 

Dr. med. Isabelle Huynh-Bui (Klinikzentrum Dortmund) 

Plastische Chirugie in Entwicklungsländern 

-85- 

WORKSHOPS and CONFERENCES


-86-

Part V 

Personnel & On the Road 

Members of the Institute 

Secretarial Office 

Claudia Wulf Secretary 

Bahar Öztamur Secretary 

Hanna Hantusch SFB491 Secretary 

Members of EP IV 

PERSONNEL 

Radu Abrudan, Dr. Instrument Scientist, ALICE 

Frank Brüssing PhD student 

Stefan Buschhorn PhD student 

Derya Demirbas Diploma student 

Anton Devishvili Instrument Scientist, Super ADAM 

Astrid Ludwig (previously: Ebbing) PhD student 

Melanie Ewerlin PhD student 

Sabine Erdt-Böhm Technician 

Mathias Gehlmann Master student 

Dimitrii Gorkov PhD student 

David Greving Master student 

Katherine Gross PhD student 

Philipp Gutfreund PhD student 

Miriam Lange Master student 

Min-Sang Lee PhD student 

Timo Lichtenstein Master student 

Jörg Meermann Technician 

Siegfried Methfessel, Prof. Dr. Emeritus 

Durga Mishra PhD student 

Mohamed Obaida PhD student 

Oleg Petracic, PD Dr. Group leader, nanostructures 

Jürgen Podschwadek Technician 

Ruslan Salikhov, Dr. Post-Doc 

Matthias Schlottke Master student 

Alexandra Schumann PhD student 

Kaveh Shokuie, Dr. Post-Doc 

Mathias Stadlbauer Master student 

Peter Stauche Engineer 

Philipp Szary PhD student 

Evgenij Termer Research assistant, webmaster 

Boris P. Toperverg, Prof. Dr. Group leader, Polarized neutron scattering 

Kurt Westerholt, Prof. Dr. Group leader, Transport 

Kirill Zhernenkov PhD student 

Hartmut Zabel, Prof. Dr. Dr. h.c. Chair 

-87-


Surface Physics Group 

Elisabeth Bartling Technician 

Wera Fehl Diploma student 

Lina Elbers Bachelor student 

Sebastian Frey PhD student 

Yu Gao Master student 

Carsten Godde PhD student 

Christian Klump Bachelor student 

Ulrich Köhler, Prof. Dr. Group leader, Surface Physics 

Martin Kroll PhD student 

Cornelia Leschke Technician 

Sani Noor PhD student 

Dietmar Rother Bachelor student 

Academic degrees 

Bachelor of Science 

Lina Elbers 

Thesis: Struktur und magnetisches Anisotropieverhalten von Fe3Si-Schichten auf GaAs(001) 

Advisor: Prof. Dr. U. Köhler 

July 2011 

Christian Klump 

Thesis: Konstruktion eines Kerr-Mikroskops mit Einsatzmöglichkeit im Ultrahochvakuum 


August 2011 

Dietmar Rother 

Thesis: Aufbau und Inbetriebnahme eines Rastertunnelmikroskops an einem Elektronenenergieverlust- 

Spektrometer 


May 2011 

Diploma/Master 

Mathias Stadlbauer 

Entwurf und Konstruktion einer integrierten MOKE-Messeinrichtung für die simultane Charakterisierung 

der magnetischen Eigenschaften nanostrukturierter Festkörper 

Advisor: Prof. Dr. Dr. h.c. Hartmut Zabel 

Co-Advisor: PD Dr. Oleg Petracic 

Date of submission (Diploma thesis): April 5, 2011 

Miriam Lange 

Magnetization and Transport Properties of Nanofabricated Magnetic Networks 

Advisor: PD Dr. Oleg Petracic 

-88-

Co-Advisor: Prof. Dr. Dr. h.c. Hartmut Zabel 

Date of submission (Master thesis): Dec. 12, 2011 

Yu Gao 

Thesis: Construction of a Kerr-microscopy system for ultra high vacuum 

Advisor: Prof. Dr. H. Köhler 

Date of submission (Master thesis): January 2011 

PERSONNEL 

Wera Fehl 

Thesis: Experimente zur Spininjektion über die Spaltkanten von GaAs-LED-Strukturen 

Advisor: Prof. Dr. H. Köhler 

Date of submission (Master thesis): March 2011 

Ph.D. Thesis 

Philipp Gutfreund 

The microscopic origin of surface slip: A neutron and x-ray scattering study on the near surface 

structure of owing liquids 

Advisor: Dr. Max Wolff 


Day of Disputation: May 15, 2011 

Alexandra Schumann 

Magnetkraftmikroskopie an lateral strukturierten magnetischen Dipolgittern: Ummagnetisierungs- 

Prozesse, Ordnung und Frustration in Honigwabenstrukturen 


Co-Advisor: Prof. Dr. Kurt Westerholt 

Day of Disputation: July 11, 2011 

Stefan Buschhorn 

Element resolved magnetization dynamics 


Co-Advisor: Prof. Dr. Kurt Westerholt 

Day of Disputation: July 15, 2011 

Mohamed Obaida 

Thesis: Magnetoresistance and Anomalous Hall Effect of Cu2MnAl, Co2MnSi and Co2MnGe 

Heusler alloy thin films 

Advisor: Prof. Dr. Kurt Westerholt 


Day of Disputation: Dec. 15, 2011 

Guests at the Institute 

Björgvin Hjörvarsson, Prof. Dr. 

Iliz Garifullin, Prof. Dr. 

Giovanni Badini Confalonieri, Dr. 

-89-


Excursions 

Aug. 18, 2010 

Visit at the Röntgen museum and climbing tour 

This time we combined informative input and sports by visiting first the well-known Röntgen 

museum in Remscheid and then continuing in a climbing garden. 

-90-

ON THE ROAD 

On the road - Visits and Experiments at external facilities 

by members of the Institute 

HASYLAB/DESY, Hamburg 

D. Mishra, D. Greving, G.A. Badini Confalonieri, J. Perlich, O. Petracic 

GISAXS studies on iron oxide nanoparticle superlattices (Sept. 9 - Sept. 12, 2011) 

Helmholtz Centre Berlin for Materials and Energy, Berlin 

Frank Brüssing, Chen Luo, Katherine Gross, Ruslan Salikhov, Radu Abrudan 

Laterally structured spin valve system with one tuneable magnetic layer (January 30 - February 

21, 2011) 

Frank Brüssing, Timo Lichtenstein, Melanie Ewerlin, Astrid Ludwig, Radu Abrudan 

Laterally structured spin valve system with one tuneable magnetic layer (July 25 -August 7, 

2011) 

Melanie Ewerlin, Derya Demirbas 

PEEM measurements on PdFe nanodot arrays (December 7, 2011) 

ILL, Grenoble, France, SuperADAM Reflectometer 

D. Mishra, V. Siong, A. Devishvili, K. Theis-Bröhl, B. P. Toperverg, H.Zabel 

PNR of iron oxide nanoparticle multilayer and monolayer (August 1 - 6 and September 29 - 

October 2, 2011) 

Dmitry Gorkov, Kirill Zhernenkov, Boris Toperverg 

Spin-flop transition in laterally patterned exchange coupled Fe/Cr multilayers via AC-PNR 

(May 16 - 21, 2011) 


AC-PNR from AF coupled Fe/Cr/Fe trilayer (May 21 - 26, 2011) 


Application of Time Resolved AC-PNR for studying domain kinetics in the patterned Fe film 

(July 08 - 28, 2011) 

Kirill Zhernenkov, Dmitry Gorkov, Boris Toperverg 

Neutron wave guides in a switched magnetic field: Proof of principle experiment (September 

05 - 10, 2011) 


AC PNR measurements of laterally patterned monocrystalline thin Fe films (September 24 - 29, 

2011) 


Kinetics of spin-flop re-orientation in laterally patterned exchange coupled Fe/Cr/Fe tri-layers 

(November 5 - 15, 2011) 


Lateral magnetic patterns in CoPt film with perpendicular anisotropy (November 16 - 20, 2011) 

-91-



AC PNR measurements of laterally patterned monocrystallyne thin Fe films (November 21 - 23, 

2011) 

Salikhov Ruslan, Dmitry Gorkov, Kirill Zhernenkov, Boris Toperverg 

AC PNR measurements of Co/Cu/Py spin valve systems (November 28 - December 08, 2011) 

ILL, Grenoble, France, IN22, three-axis spectrometer 


Thermal and AC field stimulated spin waves in Heusler alloys probed with inelastic polarized 

neutron scattering (October 09 - 20, 2011) 


MIEZE-REFLECTOMETRY: application to the domain walls kinetics (December 09 - 22, 2011) 

ILL, Grenoble, France, D22 instrument 

K. Theis-Bröhl, D. Mishra, B. Vogel, V. Siong, A. Hütten, B. P. Toperverg, A. 

Devishvili, A. Wiedenmann, H. Zabel 

GISANS of iron oxide nanoparticle monolayers at D22 (July 4 - 6, 2011) 

-92-

Part VI 

Press & Alumni News 

Alumni News 

News 

Prof. Dr. Katharina Theis-Bröhl has received a Teaching Award from the University Bremerhaven. 

This award recognizes her outstanding achievements as a lecturer of Physics, Mathematics, 

and Materials Sciences. Her students selected her as the best teacher because of her lively 

teaching style and the variety of methods and demonstrations, which she uses in her lectures. 

Moreover she is able to motivate her students and raise interest in the topics of her lectures. 

Dr. Andreas Stierle, PhD 1996, Ruhr-Universität Bochum, and previously Research Associate 

at the Max Planck Institute in Stuttgart, then W2 Professor at the Bergische Universität Siegen, 

has accepted a Professorship in the Department of now received a call from the University 

Hamburg to a W3 Professorship. 

Prof. Dr. Dr. h.c. Hartmut Zabel receives the award of ”Outstanding Referee 2011 of the 

American Physical Society”. 

-93-


-94-

Condensed Matter Physics Surface Physics - Experimentalphysik IV ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?