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1 st International Workshop on
Spin-Orbit Induced Torque
ABSTRACTS
February 24 – 27, 2013
Spintronics Group, MSE
King Abdullah University of Science and Technology (KAUST)
Thuwal, Kingdom of Saudi Arabia

Through Inspiration, Discovery

ACKNOWLEDGEMENTS
The 1st International Workshop on Spin-Orbit Induced Torque
has been made possible by the financial support from KAUST’s
Office of Competitive Research Funding (OCRF) through
the Conference and Workshop Progam. We also thank the
President's Office and the department of Event Management
for their valuable support.

1 st International Workshop on
Spin-Orbit Induced Torque
Local Organizing Committee
Aurelien Manchon, Assistant Professor, MSE, KAUST (Chair)
Udo Schwingenschlogl, Associate Professor, MSE, KAUST
Jurgen Kosel, Assistant Professor, EE, KAUST
Xixiang Zhang, Imaging and Characterization Core labs, KAUST
International Scientific Committee
Stuart Parkin, Professor & research direction, IBM Almaden, US
Mark Stiles, research director, NIST, US
Mihai Miron, researcher, Spintec, France
Kyung-Jin Lee, Professor, Korea University, Korea
7

Spin-orbit Torque Workshop
February 24 – 27, 2013
Level 0 Auditorium Between Ibn Al-Haytham and Ibn Sina (Buildings 2 and 3)
Program Schedule
Sunday, February 24
Monday, February 25 Tuesday, February 26 Wednesday, February 27
8:30a.m. Breakfast
8:50a.m.
Opening Remarks
Jean Frechet
KAUST VP Research
Chair: H. Yang Chair: S.-H. Yang Chair: X. Wang
9:00-9:35 a.m.
M. Hayashi
NIMS, Japan
8:45-9:20 a.m.
H. Ohno
RIEC-Tohoku, Japan
8:45-9:20 a.m.
A.H. MacDonald
UT Austin, US
9:35-10:10 a.m.
H.W. Lee
Postech, Korea
10:10-10:45 a.m.
A. Thiaville
LPS, France
9:20-9:55 a.m.
M.D. Stiles
NIST, US
9:55-10:30 a.m.
H. Swagten
TU Eindhoven, Netherlands
9:20-9:55 a.m.
A. Fergusson
Cambridge, UK
9:55-10:30 a.m.
H. Li
KAUST, KSA
09:30 a.m.-10:30 a.m.
Core Labs tour
Coffee Break
Chair: K. Hals Chair: F. Freimuth Chair: P. Haney
11:00 -11:35 a.m.
X. Wang
KAUST, KSA
Coffee Break
10:45-11:20 a.m.
H. Yang
NUS, Singapore
Coffee Break
10:45-11:20 a.m.
M. Fischer
Cornell, US
11:35 a.m.-12:10 p.m.
F. Freimuth
Julich, Germany
11:20-11:55 a.m.
P. Haney
NIST, US
11:20-11:55 a.m.
C. Ortiz Pauyac
KAUST, KSA
12:10 -12:45 p.m.
G. Beach,
MIT, US
11:55 a.m.-12:30 p.m.
J. Wunderlich
Prague, CzR/Cambridge, UK
11:55 a.m.-12:30 p.m.
K.J. Lee,
Korea U., Korea
Lunch
Chair: K. Garello
Lunch
Chair: E. Villanova
Lunch
Chair: M. Yamanouchi
Lunch
2:15-3:05 p.m.
A. Fert,
CNRS-Thales, France
2:00-2:50 p.m.
S.S.P. Parkin
IBM Almaden, US
2:00-2:50 p.m.
Gaudin
Spintec, France
3:05-3:40 p.m.
C.F. Pai,
Cornell, US
2:50-3:25 p.m.
E. Fullerton
UCSD, US
2:50-3:25 p.m.
K. Hals
Nordheim, Norway
3:40-4:15 p.m.
S. Grytsyuk,
KAUST, KSA
3:25-4:00 p.m.
K. Garello
ICN, Spain
3:25-4:00 p.m.
S. Demokritov
Muenster U., Germany
11a.m.-03:00 p.m.
Snorkeling Tour
Coffee Break
Coffee Break
Coffee Break
4:30-5:15 p.m.
Discussion
Chair: M.D. Stiles, NIST
4:15-4:45 p.m.
Discussion
Chair: K.J. Lee, Korea U.
4:15-5:00 p.m.
Discussion
Chair: M. Miron, SPINTEC
Break
Break
Break
Free Time-
Poster Session
5:15 p.m.
President’s Distinguished
Lecture by Albert Fert
Auditorium, bdg 20
5:15-6:45 p.m.
Poster session
Chair: F. Dogan
7:30 p.m.
Welcome Dinner
Marina–Al Marsa
7:30 p.m.
Bowling night
7:30 p.m.
Gala Dinner
Thuwal Sayeed
Fish restaurant
8

Spin-Orbit Induced Torque Workshop 2013
International Invited speakers
NAME
Geoffrey Beach
Sergej Demokritov
Andrew Ferguson
Albert Fert
Mark Fischer
Frank Freimuth
Eric Fullerton
Sergiy Grytsyuk
Kevin Garello
Gilles Gaudin
Kjetil Hals
Paul Haney
Masamitsu Hayashi
Hyun-Woo Lee
Kyung-Jin Lee
Hang Li
Allan MacDonald
Hideo Ohno
Christian Ortiz Pauyac
Chi-Feng Pai
Stuat Parkin
Mark Stiles
Henk Swagten
Andre Thiaville
Joerg Wunderlich
Xuhui Wang
Hyunsoo Yang
Institution
MIT, US
University of Muenster, Germany
Cambridge University, UK
CNRS-Thales, France
Cornell University, US
Forschungszentrum Jülich, Germany
UCSD, US
KAUST, Saudi Arabia
Universitat Autonoma de Barcelona, Spain
SPINTEC, France
Trondheim University, Norway
NIST, US
NIMS, Japan
POSTECH University, Korea
Korea University, Korea
KAUST, Saudi Arabia
UT Austin, US
RIEC/Tohoku University, Japan
KAUST, Saudi Arabia
Cornell University, US
IBM-Almaden, US
NIST, US
TU Eindhoven, The Netherlands
Laboratoire de Physique du Solide, Orsay, France
Cambridge, UK & ASCR, Prague
KAUST, Saudi Arabia
National University of Singapore, Singapore
9

10
ORAL PRESENTATIONS

Current induced spin orbit torques
in magnetic heterostructures
Masamitsu Hayashi 1
1 National Institute for Materials Science, Tsukuba 305-0047, Japan
‎*email of presenting author: hayashi.masamitsu@nims.go.jp
We would like to present our latest findings on current induced torques in Ta|CoFeB|MgO magnetic heterostructures[1]. Ultrathin
magnetic heterostructures exhibit a variety of rich physics owing to the strong effects from the interfaces. Power efficient current
induced magnetization switching and domain nucleation, fast current driven domain wall motion have been observed in such
systems. Most of the current (or voltage) induced effects in these systems can be represented by the “effective magnetic fields”,
which illustrate the strength and direction of the torque exerted on the magnetic moments. A comprehensive understanding of
the effective fields is key to the development of magnetic nano-devices aimed for memory and logic applications.
A low current lock-in detection scheme is used to evaluate the effective field vector. The CoFeB layer is perpendicularly magnetized
owing to the interface magnetic anisotropy of CoFeB|MgO. We find that the effective field is very sensitive to the thickness of the
Ta and CoFeB layers. The effective field even changes its direction when the Ta layer thickness is varied, indicating that there are
competing effects that contribute to the effective field generation. We discuss our results in light of the spin Hall effect and an
effect due to Rashba-like Hamiltonian.
Acknowledgment: FIRST program
[1] J. Kim et al., Nature Mater. (2013) in press.
11

Rashba spin-orbit coupling in a
magnetic bilayer: Roles of orbital
angular momentum
Jin-Hong Park 1 , Choong H. Kim 2 , Hyun-Woo Lee 3 *, and Jung Hoon Han 1
1 Department of Physics, Sungkyunkwan University, Suwon 440-746, Korea
2 Department of Physics and Astronomy, Seoul National University, Seoul 151-742, Korea
3 Department of Physics, POSTECH, Pohang, Kyungbuk 870-784, Korea
‎*email of presenting author: HWL@postech.ac.kr
Rashba spin-orbit coupling α R σ . (k x ẑ) arises when the inversion symmetry is broken near an interface. Despite large amount of
literature on the Rashba spin-orbit coupling, its study on magnetic systems is very rare [1]. In order to examine the magnitude and
characteristics of the Rashba spin-orbit coupling in a magnetic bilayer that consists of an ultrathin 3d magnetic layer in contact
with a non-magnetic heavy metal layer, we study theoretically the electronic structure of the bilayer. Our first-principles calculation
[2] indicates that many energy bands of the bilayer may possess large Rashba parameter α R of order 1 eV . A. We identify two crucial
factors for the large α R : momentum-dependent ordering of atomic orbital angular momentum and strong orbital hybridization in
the bilayer. Interestingly, the sign of α R varies from energy bands to energy bands. We argue that average α R relevant for electron
transport properties will thus depend sensitively on exactly which bands are located at the Fermi energy. In particular, if multiple
bands at the Fermi energy make mutually cancelling contributions, the average α R may be much smaller than 1 eV . A. If time allows,
we also discuss briefly implications of the Rashba spin-orbit coupling on the spin torque and other magnetic properties.
12

On the role of Dzyaloshinskii
domain walls in ultrathin
magnetic films
André Thiaville 1 *, Stanislas Rohart 1 , Emilie Jué 2 , Vincent Cros 3 , Albert Fert 3
1 Laboratoire de Physique des Solides, Université Paris-sud, CNRS UMR 8502, Orsay, France
2 SPINTEC, Institut Nanosciences et Cryogénie, UMR CEA-CNRS-INPG-UJF, Grenoble, France
3 Unité Mixte de Physique CNRS-Thales and Université Paris-sud, Palaiseau, France
‎*email of presenting author: andre.thiaville@u-psud.fr
We have explored a new type of domain wall structure in ultrathin films with perpendicular anisotropy, as a consequence of the
existence of a Dzyaloshinskii-Moriya interaction (DMI) due to the adjacent layers. This study was performed by numerical and
analytical micromagnetics. The results show that these walls can, depending on the value of the DMI constant, move in stationary
conditions at large velocities under large fields. These walls also show interesting properties of current-induced domain wall
motion under the spin Hall effect. Even if these walls look like Néel walls in statics (for large enough DMI), their dynamics is
unique. Thus we propose to call them Dzyaloshinskii domain walls [1].
An important aspect of this work is that we have considered the Fert form [2] of the DMI induced by an adjacent layer, that reads
in continuous form
where z is the film normal direction (oriented from the adjacent layer to the film), (m) the unit magnetization vector, and D (units
J/m2) the DMI constant in micromagnetic notation. This form is different from the `bulk’ form of DMI usually considered for
materials without inversion symmetry [3], but corresponds to what has been observed by spin-polarized STM [4], and leads to
magnetization cycloids rather than helixes. In other words, this form of the DMI leads to Néel-like domain walls.
[1] A. Thiaville, S. Rohart, E. Jué, V. Cros, A. Fert, Europhys. Lett. 100, 57002 (2012).
[2] A. Fert, Mater. Science Forum 59-60, 439 (1990); A. Fert, P.M. Levy, Phys. Rev. Lett. 44, 1538 (1980).
[3] for an introduction, see A.N. Bogdanov, U.K. Rössler, Phys. Rev. Lett. 87, 037203 (2001).
13

Spin-hall Conductivity and
Electric Polarization in Metallic
Thin Films
Xuhui Wang, 1 Jiang Xiao , 2, 3 Aurelien Manchon, 1 and Sadamichi Maekawa 4, 5
1 King Abdullah University of Science and Technology (KAUST), Physical Science and Engineering Division, Thuwal 23955-6900, Saudi Arabia
2 Department of Physics and State Key Laboratory of Surface Physics, Fudan University, Shanghai 200433, China
3 Center for Spintronic Devices and Applications, Fudan University, Shanghai 200433, China
4 Advanced Science Research Center, Japan Atomic Energy Agency, Tokai 319-1195, Japan
5 CREST, Japan Science and Technology Agency, Tokyo 102-0075, Japan
In a normal metallic thin film (without bulk spin-orbit coupling, such as Cu or Al) is sandwiched by two insulators, the
potential gradients at the interfaces give rise to a Rashba type interfacial spin-orbit coupling. Our theoretical studies
reveal that two prominent effects arise due to such an interfacial spin-orbit coupling: a giant spin-Hall conductivity due
to the surface scattering and a transverse electric polarization due to the spin-dependent phase shift in the spinor wave
functions. More interestingly, the spin-Hall conductivity is independent of microscopic details of the interfacial spin-orbit
coupling. The electric polarization, manifesting itself as a Hall efffect in the absence of magnetic field and magnetism, is
along the confinement direction that is unique to the multilayer structure while absent in any two-dimensional systems.
We also discuss the experimental method towards detection of the electric polarization.
14

Ab initio study of Spin-Orbit
Torques in inversion asymmetric
Magnetic Layers
Frank Freimuth, Yuriy Mokrousov, Stefan Blügel
Peter Grünberg Institut & Institute for Advanced Simulation,
Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
f.freimuth@fz-juelich.de
Several recent experiments [1,2,3,4,5] have shown that an in-plane current can switch magnetization of thin ferromagnetic
metallic layers asymmetrically sandwiched between an oxide layer on one side and a paramagnetic metal layer on the other. The
current induced torques in these experiments stem both from the spin-Hall effect (SHE) of the paramagnetic metal layer, which
injects a spin-current into the ferromagnetic metal, and from the Rashba effect, due to which the charge carriers experience an
in-plane spin-orbit field.
The microscopic origin of the current induced torques in these systems is currently only poorly understood, especially because the
magnitude of the effective Rashba interaction has not been measured directly in the experiments, making estimations based on
the Rashba model difficult. Moreover, models that consider contributions both due to SHE and due to the Rashba effect on an
equal footing are difficult to construct.
In this presentation we discuss density-functional theory calculations of the current-induced torques in Pt/Co/X heterostructures
(X=Vacuum, or Al, or O, or AlO). In agreement with experiments, our calculations show the presence of two geometrically distinct
torque components, a field-like one corresponding to a current-induced effective magnetic field in the plane of the magnetic layer,
and an STT-like one allowing to switch the magnetization reversibly between the two perpendicular configurations. Both torque
components arise partly from the SHE and partly from the Rashba effect. We find that while the current-induced in-plane effective
magnetic field is almost negligible in Pt/Co/Vacuum, it becomes sizeable if Al, O, or AlO are deposited on Co. Likewise, our
calculations of the STT-like component are in good agreement with experiments. Moreover, by determining the spin-current in the
perpendicular direction layer resolved and by switching off the spin-orbit interaction in the Co layer we disentangle contributions
from the Rashba effect and contributions due to SHE. It is found that both mechanisms contribute in realistic systems and can
generally be of the same order of magnitude.
[1] Miron et al., Nature Mat. 9, 230 (2010)
[2] Miron et al., Nature 476, 189 (2011)
[3] Liu et al., arXiv: 1110.6846
[4] Liu et al., Science 336, 555 (2012)
[5] Pi et al., APL 97, 162507 (2010)
15

Domain wall motion via
interfacial spin-orbit torques
S. Emori​ 1 , U. Bauer 1 , S.-M. Ahn 1 , and G. S. D. Beach 1 *
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, US
‎*email of presenting author: gbeach@mit.edu
Current-controlled displacement of domain walls (DWs) in ferromagnetic nanowires underpins the operation of an emerging class
of spintronic memory and logic devices. In ultrathin ferromagnets sandwiched between an oxide and a heavy metal, currentinduced
DW motion is anomalously efficient [1,2]. This observation has been widely attributed to a Rashba effective field that
stabilizes Bloch DWs against deformation, permitting high-speed motion via conventional spin-transfer torque [1]. However, the
spin Hall effect in the heavy metal has recently been shown strong enough to induce magnetization switching [3], which suggests
that it likewise plays a key role in current-induced DW motion [4,5]. We will show that current alone drives DWs with high
efficiency in both Pt/CoFe/MgO and Ta/CoFe/MgO nanowires, but the direction of motion depends on the sign of the spin Hall
angle of the underlayer. We directly measure the Slonczewski-like torque due to the spin Hall effect via magnetization tilting
measurements, and find it to be consistent with previously-reported spin Hall angles for Pt and Ta [3]. The magnitude of the
measured Slonczewski-like torque agrees well with the effective field extracted from current-driven DW motion measurements,
but the symmetry of this torque precludes it from driving the Bloch DWs that are expected from magnetostatic considerations. We
show experimentally that the recently-proposed Dzyaloshinskii-Moriya interaction [6] provides the missing ingredient, stabilizing
Néel DWs with a fixed chirality to permit robust current-driven motion in a fixed direction.
[1] I.M. Miron et al. Nat. Mater. 9, 230 (2010); ibid 10, 419 (2011).
[2] S. Emori et al. Appl. Phys. Lett. 101, 042405 (2012).
[3] L. Liu, et al., Science 336, 555–558 (2012); L. Liu et al. Phys. Rev. Lett. 109, 096602 (2012).
[4] K.–W. Kim, et al., Phys. Rev. B 85, 180404 (2012); X. Wang & A. Manchon, arXiv:1111.5466 (2011).
[5] P.P.J. Haazen, et al., arXiv:1209.2320 (2012).
[6] A. Thiaville et al. Europhys. Lett. 100, 57002 (2012).
16

Spin-orbitronics
A.Fert 1 , V. Cros 1 , C. Deranlot 1 , J-M. George 1 , J. Grollier 1 , H. Jaffres 1 , N. Reyren 1 ,
J. Sampaio 1 ,Y. Kawanishi 2 , Y. Niimi 2 , Y. Otani 2,3 , D.-H. Wei 2 , M. Chshiev 4 ,
H.-X. Yang 4 , T. Valet 5 , J.P. Attané 6 , P. Laczkowski 6 , J.C. Rojas Sanchez 6 , L. Vila 6 ,
A.V. Khvalkovskiy 7 , J-M De Teresa 8 , P.M. Levy 9 .
1 UMP CNRS-Thales and Université Paris-Sud, 1 AV. A. Fresnel, Palaiseau, 91767, France
2 Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba, Japan.
3 RIKEN-ASI, Wako, Saitama, Japan.
4 SPINTEC, UMR-8191, CEA/CNRS/UJF/GINP,38054 Grenoble, France.
5 In Silicio SAS, 13857 Aix en Provence Cedex 3, France.
6 INC, CEA, 38054, Grenoble, France
7 Grandis, Inc., 1123 Cadillac Court, Milpitas, California 95035, U.S
8 ICM,Univ-Zaragoza-CSIC,Spain
9 New York University,New York, US
e-mail: albert.fert@thalesgroup.com
I will review recent advances on Spin-Orbit effects in nonmagnetic metallic materials and at interfaces.
a) Dzyaloshinsky-Moriya interactions at metallic interfaces [1-2] and generation of magnetic skyrmions [2].
b) Very large Spin Hall Effect (SHE) generated by heavy impurities in simple metals: experiments (Spin Hall angle = - 0.24 for
0.5% Bi in Cu) and theory [3].
c) Rashba and Edelstein-Rashba [4] effects at metallic interfaces, observation of the Inverse Edelstein-Rashba effect induced
by the Bi/Ag interface.
d) Current-induced motion of skyrmions (or domain walls) using SHE and Rashba effect [5].
[1] A. Fert, Metallic Multilayers, Materials Science Forum 59-60, Trans. Tech. Publ. (1990), p.440.
[2] S. Heinze et al, Nature Physics 7 (2011), 713
[3] Y. Niimi et al, PRL 106, 126601 (2011)
[4] V.M. Edelstein, Sol. Stat. Comm. 73, 233 (1990))
[5]A.V. Khvalkovskiy et al, Phys. Rev. B 87, EID e020402
17

The spin Hall effect in Tantalum
and Tungsten-based systems
Chi-Feng Pai 1 *, Luqiao Liu 1 , Yun Li 1 , H.W. Tseng 1 , Daniel C. Ralph 2 and Robert A. Buhrman 1
1 School of Applied and Engineering Physics, Cornell University, US
2 Department of Physics, Cornell University, US
‎*email of presenting author: cp389@cornell.edu
It has been shown that the spin-orbit interaction from Pt can be utilized to control the magnetization direction of an adjacent
ferromagnetic layer with an in-plane charge current [1,2]. Here we present a similar effect in Ta and W-based systems but with
an opposite spin-torque polarity and with a greater magnetization switching efficiency in comparison to that observed in Pt-based
systems [3,4]. Our results from both spin-torque ferromagnetic resonance (ST-FMR) measurements and from in-plane magnetization
spin-torque switching in three-terminal devices can be well-explained by the spin Hall effect induced spin transfer torque scenario.
From these measurements we estimate the spin Hall angle of the high resistivity ß-Ta and ß-W to be ~-0.15 and ~-0.30, respectively.
[1] I. M. Miron, K. Garello, G. Gaudin, P.-J. Zermatten, M. V. Costache, S. Auffret, S. Bandiera, B. Rodmacq, A. Schuhl,
and P. Gambardella, Nature 476 189 (2011).
[2] L. Liu, O. J. Lee, T. J. Gudmundsen, D. C. Ralph and R. A. Buhrman, Phys. Rev. Lett. 109, 096602 (2012).
[3] L. Liu, C.-F. Pai, Y. Li, H. W. Tseng, D. C. Ralph, and R. A. Buhrman, Science 336, 555 (2012).
[4] C.-F. Pai, L. Liu, Y. Li, H. W. Tseng, D. C. Ralph, and R. A. Buhrman, Appl. Phys. Lett. 101, 122404 (2012).
18

Rashba effect at the Co/ X
interfaces (X=Pt, Pd, Au, Ir, Bi,
W, Ta, and Rh). Influence of the
lattice mismatch.
S. Grystyuk, A. Belabbes, U. Schwingenschlogl, A. Manchon
King Abdullah University of Science and Technology (KAUST), Physical Science and Engineering Division,
Thuwal 23955-6900, Saudi Arabia
The development of the electronic devices, where magnetization control is realized by means of electrical currents rather than
external magnetic fields, is offering new perspectives to Spintronics. A promising way to control the magnetization direction of
spin-based devices is to exploit the spin-orbit coupling (SOC) present in the band structures of inversion-asymmetric systems. In
such structures, a specific form of spin-orbit coupling known as Rashba SOC arises and allows for the electrical generation of spin
density. Although the Rashba effect is well-known in semiconductor structures, it’s nature at metallic interfaces has only been
scarcely studied.
In the present work, we investigate the spin-splitting of the band structures of thin layers composed ferromagnetic 3d transition
metals (here, Co) and noble-metals such as Pt, Pd, Au, Ir, Bi, W, Ta, Rh. Using first principle calculation, we identify a clear Rashba
spin-splitting that depends on the structure symmetry. The strength of the Rashba spin-splitting is investigated together with the
magnetic anisotropy and magnetic properties of the system. Since lattice mismatch between such involved interface materials is
huge (more than 12%) it could has dramatic influence on Rashba effect. To investigate this, calculations have been performed for
large supercells with different density of involved elements, reducing the lattice mismatch to less than 1%. Finally implications in
terms of Rashba torque and Dzyaloshinskii-Moriya interaction will be discussed.
19

Two and three terminal
non-volatile spintronics devices
for VLSI applications
Hideo Ohno 1,2,3
1 Center for Spintronics Integrated Systems, Tohoku University,
2 Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University
3 WPI-Advanced Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan.
I start by explaining the reason why there is now a huge interest in the VLSI community on spintronics devices. Next I review the
current status of two terminal device, magnetic tunnel junction. Then, the need for three terminal switching devices that can
separate the write and read current paths particularly for logic applications is discussed along with two possible three terminal
device implementations; domain wall and the spin Hall devices. Finally I show our results on a three terminal switching device with
the channel based on an interconnection material Cu with Ir doping.
20

Spin transfer torques in
magnetic bilayers with strong
spin orbit coupling
Kyung-Jin Lee 1 , Hyun-Woo Lee 2 , Aurelien Manchon 3 , Paul M. Haney 4 , M. D. Stiles 4*
1 Korea University, Department of Material Science & Engineering, South Korea
2 PCTP and Department of Physics, Pohang University of Science and Technology, Korea
3 King Abdullah University of Science and Technology, Saudi Arabia
4 Center for Nanoscale Science and Technology, NIST, Gaithersburg, US
‎*email of presenting author: mark.stiles@nist.gov
Current driven magnetic dynamics in ferromagnetic thin films on top of non-magnetic films with strong spin orbit coupling show
strong current-induced torques. Several theoretical models have been proposed to explain these torques. In one model, the current
flowing through the non-magnetic layer gives rise to a spin Hall current, leading to a spin current incident on the interface
between the two layers. This spin current causes spin transfer torques similar to those that are important in magnetic multilayers
with current flowing perpendicular to the plane. Another model proposes a torque due to the spin-orbit coupling at the interface
where the inversion symmetry found in the bulk materials is broken. We model the spin transport with a semiclassical Boltzmann
equation approach. Both torques are present in this model and for reasonable parameter sets are largely independent of each
other. We compute the dependence of the torques on the thickness of the layers and find that it is difficult to reproduce the large
sensitivity to the thickness of the ferromagnetic layer as found in several experiments. This disagreement indicates that structural
or electronic properties are probably changing with the thickness of the films studied in experiments.
21

Domain-wall depinning
governed by the spin Hall effect
Henk Swagten*, Pascal Haazen, Elena Murè, Jeroen Franken, Reinoud Lavrijsen,
Bert Koopmans
Department of Applied Physics, Eindhoven University of Technology
Center for NanoMaterials and COBRA Research Institute,
P.O. Box 513, 5600 MB Eindhoven, The Netherlands
‎*email of presenting author:h.j.m.swagten@tue.nl
Current induced domain wall motion (CIDWM) in perpendicular materials is believed to be very efficient. In this work, we will show
that the Spin Hall effect (SHE) [1,2] provides a radically new mechanism for CIDWM in these systems. Using focused-ion-beam
irradiation we are able to stabilize and pin two DWs in a Pt / Co / Pt nanowire. By depinning the DWs under the application of a
perpendicular field as well as an injected charge current and in-plane magnetic field, we are able to disentangle the contributions
to DW motion originating from conventional spin transfer torques that act on magnetization gradients and from the hitherto
unexplored Spin Hall effect torques [3].
Data will be presented on the perpendicular depinning fields as a function of charge current for the two DWs of a single domain,
with an in-plane field along the current direction. The fact that we find equal slopes for the depinning field versus current for both
DWs, as well as a sign change of the slope when we change the polarity of the DWs, clearly indicates the dominance of the SHE
contribution. To further proof that the SHE is dominating the depinning process, we have tuned the internal spin structure of the
DW (from Bloch to Néel) by varying the in-plane field parallel to the current, and find that the influence of current on the
depinning is highest when the DW has the Néel structure, while it is virtually absent in the Bloch case. This behavior is verified by
macrospin simulations as well as by measurements of the DW resistance at variable in-plane magnetic field.
As a final evidence for the dominance of the SHE, we have varied the thickness of the bottom and top Pt, by which we are able to
tune the spin Hall currents originating from the nonmagnetic Pt layers. Indeed, the slope of the depinning field versus current is
changing sign when we change Pt (4 nm) / Co (0.5 nm) / Pt (2 nm) to an inverted stack of Pt (2 nm) / Co (0.5 nm) / Pt (4 nm), and
vanishes for Pt (3 nm) / Co (0.5 nm) / Pt (3 nm) when the spin Hall currents effectively cancel.
[1] I. M. Miron et al., Nature 476, 189 (2011).
[2] L. Liu et al., Science 336, 555 (2012).
[3] P.P.J. Haazen et al., Nature Materials, in press (2013).
22

Comparison of current induced
torques in various magnetic wires
Hyunsoo Yang
1 Department of Electrical and Computer Engineering, National University of Singapore, Singapore
‎*email of presenting author:eleyang@nus.edu.sg
Recently, a novel method to manipulate magnetization by in-plane current injection via the spin-orbit coupling in metal/
ferromagnetic/oxide trilayers has been reported and gained great interests. We have studied current-induced torques in
ferromagnetic nanowires made of Co/Pd multilayers, Pt/CoFeB/MgO, and Ta/CoFeB/MgO with a perpendicular magnetic anisotropy.
In case of Co/Pd multilayers, using Hall voltage measurements and lock-in characterization, it is found that upon injection of an
electric current in a uniformly magnetized sample, both in-plane (Slonczewski-like) and perpendicular (field-like) torques build up
in the nanowire. The ratio between the torques is found to be between 1 and 2, and the total torque has an effective field of
~ 250 Oe/mA . We theoretically show that this observation cannot be explained solely by spin Hall effect-induced torque, indicating
a probable contribution of band-structure related spin-orbit torques. In case of Pt/CoFeB/MgO in-plane torque dominates, while
both in-plane and perpendicular torques coexist in Ta wires. The role of multilayer structures will be discussed as well.
23

First principles calculations
of current-induced torques
in magnetic bilayers
Paul Haney 1 , Mark Stiles 1 , Kyung-Jin Lee 2 , Hyun-Woo Lee 3 , Aurelien Manchon 4
1 Center for Nanoscale Science and Technology, NIST, Gaithersburg, US
2 Korea University, Department of Material Science & Engineering, South Korea
3 PCTP and Department of Physics, Pohang University of Science and Technology, Korea
4 King Abdullah University of Science and Technology, Saudi Arabia
Current-induced torques on magnetic systems can be driven by spin-orbit coupling. Experiments on thin films with a Co layer
deposited on a heavy metal layer (e.g. Pt, Ta) demonstrate that these spin-orbit torques are substantial, and depend strongly on
system parameters such as the Co film thickness. To elucidate the origin and properties of these torques, we perform 1 st -principles
calculations of the Rashba-like spin-orbit coupling and resulting “field-like” current-induced torque present at a X-Co interface
(X=Cu, Ag, Au, Pt). The magnitude of this torque shows nontrivial angular dependence, and is also very sensitive to the thickness
of the Co layer. The Co thickness dependence can be understood using a tight-binding model in the current-perpendicular to plane
geometry. We also briefly discuss the calculation of spin hall currents in the context of the Landauer formalism.
24

Piezo-electric control of the
mobility of a domain wall
driven by adiabatic and
non-adiabatic torques
E. De Ranieri 1 , P. E. Roy 1 , D. Fang 1,2 , E. K. Vehsthedt 3,4 , A. C. Irvine 2 , D. Heiss 2 ,
A. Casiraghi 5 , R. P. Campion 5 , B. L. Gallagher 5 , T. Jungwirth 3,5 , and J. Wunderlich 1,3 *
1 Hitachi Cambridge Laboratory, JJ Thomson Avenue, Cambridge, CB3 0HE, UK
2 Microelectronics Group, Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK
3 Institute of Physics ASCR, v.v.i., Cukrovarnicka' 10, 162 53 Praha 6, Czech Republic
4 Department of Physics, Texas A&M University, College Station, TX 77843-4242, US
5 School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK
‎*email of presenting author: jw526@cam.ac.uk
Rich internal degrees of freedom of magnetic domain walls make them an attractive com- plement to electron charge for exploring
new concepts of storage, transport, and processing of information. [1–3] We utilize the tunable internal structure of a domain wall
in perpendicularly magnetized GaMnAsP/GaAs ferromagnetic semiconductor and demon- strate devices in which piezo-electrically
controlled magnetic anisotropy yields up to 500% mobility variations for an electrical-current driven domain wall. [4–6] We
observe current in- duced domain wall motion in both the steady state and precessional regimes [7] and report a direct observation
of the Walker breakdown separating the two regimes with different mobilities. The piezo-electric control of the domain wall
mobility is realized by controlling the Walker breakdown critical current. Our work demonstrates that in spin-orbit coupled
ferromagnets with weak extrinsic domain wall pinning, the piezo-electric control allows to experimentally assess the characteristic
ratio of adiabatic and non-adiabatic spin transfer torques in the current driven domain wall motion. [8]
[1] Chappert, C., Fert, A. & Dau, F. N. V., Nature Mat. 6, 813 (2007).
[2] Parkin, S. S. P., Hayshi, M. & Thomas, Science 320, 190 (2008).
[3] Allwood, D. A. et al., Science 309, 1688 (2005).
[4] Berger, J. Appl. Phys. 55, 1954 (1984).
[5] Freitas, P. P. & Berger, J. Appl. Phys. 57, 1266 (1985).
[6] Yamaguchi, A. et al., Phys. Rev. Lett. 92, 077205 (2004).
[7] Mougin, A., Cormier, M., Adam, J. P., Metaxas, P. J. & Ferre, EPL 78, 57007 (2007).
[8] D. Ralph and M. Stiles and S. Bader, J. Magn. Magn. Mater. 320, 1189 (2008).
25

Current driven domain wall
dynamics controlled by proximity
induced interface magnetization
Stuart Parkin
IBM Almaden Research Center, San Jose, Californjia, US
‎stuart.parkin@us.ibm.com
Ultra-thin perpendicularly magnetized nanowires are the ideal medium for high-density memory and logic devices based on
magnetic domain walls. Recently it has been reported that domain walls can be driven by current at very high speed in such
nanowires[1]. The high velocity and the direction of motion of the domain walls are inconsistent with conventional theories based
on transfer of spin angular momentum from the current. Here we show in nanowires formed from atomically thin Co and Ni layers
that interfaces with specific metal layers control both the speed and direction of the domain walls[2]. These layers are formed from
non-magnetic metals, namely Pt, Pd and Ir, which become magnetic in proximity to strong ferromagnets. When the induced
moment is suppressed by the insertion of atomically thin Au layers the domain walls are considerably slowed. We show that the
mechanism driving the domain walls derives from the intertwined phenomena of spin Hall currents in the non-magnetic layers
and a Dzialoshinskii-Moriya interaction at the cobalt- non-magnetic interface that fixes the chirality of the domain walls[3][4].
[1] K.-S. Ryu, L. Thomas, S.-H. Yang, S.S.P. Parkin, Appl. Phys. Expr. 5 (2012) 093006.
[2] K.-S. Ryu, S.-H. Yang, L. Thomas, S.S.P. Parkin, preprint (2012).
[3] L. Thomas, K.-S. Ryu, S.-H. Yang, S.S.P. Parkin, preprint (2013).
[4] K.-S. Ryu, S.-H. Yang, L. Thomas, A. Manchon and S.S.P. Parkin (2013).
26

Light–induced magnetization
reversal of high-anisotropy TbCo
alloy films
Sabine Alebrand 1 , Matthias Gottwald 2,3 , Michel Hehn 2 , Daniel Steil 1 , Mirko
Cinchetti 1 , Daniel Lacour 2 , Martin Aeschlimann1, Stéphane Mangin 2 ,
Yeshaiahu Fainman 3 , and Eric Fullerton 3 *
1 Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, D-67663 Kaiserslautern, Germany
2 Institut Jean Lamour UMR CNRS 7198– Université de Lorraine, Vandoeuvre-lès-Nancy, France
3 Center of Magnetic Recording Research, University of California San Diego, CA, US
‎*email of presenting author: efullerton@ucsd.edu
Magnetization reversal using circularly polarized light provides a way to
control magnetization without any external magnetic field and has the
potential to revolutionize magnetic data storage. However, in order to reach
ultra-high-density data storage, high anisotropy media providing thermal
stability are needed. Here, we describe all-optical magnetization switching
for different Tb x Co 1-x ferrimagnetic alloy compositions with anisotropy fields
reaching 6 T corresponding to anisotropy constants of 3x106 ergs/cm 3 . This
anisotropy value would enable sub 10-nm patterned islands that are
thermally stable. Using either a ps-laser (wavelength of 532 nm, FWHM at
sample position ~ 10 ps) or a fs-laser (wavelength of 780 nm, FWHM at
sample position ~ 400 fs) we observed reversible all-optical switching of the
films with changing circular polarization (Fig. 1). However, we only observe
all-optical magnetization switching in Tb x Co 1-x ferrimagnetic alloy films for
a certain composition range. This composition range corresponds to the
particular one for which the compensation temperature is between room
temperature and the Curie temperature. We will discuss the relevance of
these results for the microscopic understanding and potential applications
of all optical switching.
[1] S. Alebrand et al., Appl. Phys. Lett. 101, 162408 (2012).
Figure 1: (a): Schematic of the optical switching setup. (b) and (c):
Demonstration of AOS of a Tb 26 Co 74 film where the laser pulse
with fixed circular polarization was swept over the sample and
stripe domains were written.
27

Symmetry and magnitude
of spin-orbit torques in
ferromagnetic heterostructures
Kevin Garello 1 , Ioan Mihai Miron 2 , Can Onur Avci 1 , Frank Freimuth 3 ,
Yuriy Mokrousov 3 , Stefan Blügel 3 , Stéphane Auffret 2 , Olivier Boulle,
Gilles Gaudin 2 , and Pietro Gambardella 1,4,5
1 Catalan Institute of Nanotechnology (ICN), E-08193 Barcelona, Spain
2 SPINTEC, UMR-8191, CEA/CNRS/UJF/GINP, INAC, F-38054 Grenoble, France
3 Institut für Festkörperforschung and Institute for Advanced Simulation, Forschungszentrum Jülich, 52425 Jülich, Germany
4 Departament de Física, Universitat Autonoma de Barcelona (UAB), E-08193 Barcelona, Spain
5 Institució Catalana de Recerca i Estudis Avançats (ICREA), E-08010 Barcelona, Spain
‎*email of presenting author: kevin.garello@icn.cat
Current-induced spin torques are of great interest to manipulate the orientation of nanomagnets without applying external
magnetic fields. They find direct application in non-volatile data storage and logic devices, and provide insight into fundamental
processes related to the interdependence between charge and spin transport. Recent demonstrations of magnetization switching
induced by in-plane current injection in ferromagnetic heterostructures [1] have drawn attention to a class of spin torques based
on orbital-to-spin momentum transfer, which is alternative to pure spin transfer torque (STT) between noncollinear magnetic
layers and amenable to more diversified device functions [1,2]. Due to the limited number of studies, however, there is still no
consensus on the symmetry, magnitude, and origin of spin-orbit torques (SOTs). Here we will report on the quantitative vector
measurement of SOTs in Pt/Co/AlOx trilayers using harmonic analysis of the Hall Voltage as a function of the applied current and
magnetization direction. Based on general space and time inversion symmetry arguments, we show that asymmetric heterostructures
allow for two different SOTs having odd and even behavior with respect to magnetization reversal. We will present our experimental
results, revealing a scenario that goes beyond simple models of the spin Hall and Rashba contributions to SOTs.
[1] Miron, I. M., Garello, K., Gaudin, G., Zermatten, P.-J., Costache, M. V., Auffret, S., Bandera, S., Rodmacq, B., Schuhl, A. &
Gambardella, P. Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection Nature. 476,
189-193 (2011).
[2] Liu, L., Pai, C-F., Li, Y., Tseng, H. W., Ralph, D. C. & Buhrman, R. A. Spin torque switching with the giant spin Hall effect of
tantalum. Science. 336, 555-558 (2012).
28

President’s Distinguished Visiting Speaker
Auditorium, Building 20
Spintronics: a new frontier for
computing and communications
Albert Fert
UMP CNRS/Thales, Palaiseau and Université Paris-Sud, Orsay, France
Spin Electronics - or Spintronics – is often described as a new type of electronics exploiting the influence of the orientation of the
electron spin* on the electrical conduction. The starting point was the discovery of the “giant magnetoresistance” (GMR), a
property of magnetic multilayers that is used today to read the hard disc of our computer and has led to a large increase of the
capacity of the discs. Nowadays spintronics is developing along many novel directions with a promising perspective of applications,
short term applications for next generations of computers or telephones and, in a longer term, devices to go beyond the limits of
conventional semiconductor-based electronics.
After an introduction on the fundamentals of spintronics, I will review some of the most interesting emerging research directions.
The spin transfer phenomena will be applied soon in new types of non-volatile memories called STT-RAM (with a significant
reduction of the energy consumption in computers) and also to devices for radio-wave generation in telecommunications.
Spintronics with carbon-based materials like graphene or carbon nanotubes is foreseen to be the basis of new types of logic
circuits in the beyond-silicon perspective. The study of neuromorphic devices for bio-inspired computing is another exciting novel
direction of research.
* The spin can be described as a small magnet carried by each electron
29

Theory of Spin-Orbit Induced
Torques
Zhenhua Qiao 1 and Allan MacDonald 1*
1 Physics Department, University of Texas at Austin, US
‎*email of presenting author: macd@physics.utexas.edu
Current induced torques in magnetic systems can be understood [1] quite generally in terms of the difference between equilibrium
and the transport steady state in the spin-density induced by a given exchange potential. We apply this point of view to torques
exerted on the moments of a ferromagnetic thin film placed on the surface of a paramagnetic conductor with strong spin-orbit
interactions. We will report on a numerical non-equilibrium Greens function study of model transition metals which aims i) to
identify system parameters that can be adjusted to maximize current-induced torques, and ii) to critically analyze the degree to
which the torques can be understood solely in terms of spin-accumulation due to the spin Hall effect of the paramagnetic metal.
[1] A.S. Nunez and A.H. MacDonald, Solid State Commun. 139, 31 (2006).
30

Spin-orbit ferromagnetic
resonance
D. Fang 1 , H. Kurebayashi 1 , T. D. Skinner 1 , C. Ciccarelli 1 , J. Wunderlich 2,3 ,
K. Výborný 2† , L. P. Zârbo 2 , R. P. Campion 4 , A. Casiraghi 4 , B. L. Gallagher 4 ,
T. Jungwirth 2,4 and A. J. Ferguson 1*
1 Cavendish Laboratory, University of Cambridge, UK
2Institute of Physics ASCR, Czech Republic
3Hitachi Cambridge Laboratory, UK
4School of Physics and Astronomy, University of Nottingham, UK
†Present address: Department of Physics, State University of New York at Buffalo, US
‎*email of presenting author: ajf1006@cam.ac.uk
In conventional magnetic resonance techniques the magnitude and direction of the oscillatory magnetic field are (at least
approximately) known. This oscillatory field is used to probe the properties of a spin ensemble. Here, I will describe experiments
that do the inverse [1]. I will discuss how we use a magnetic resonance technique to map out the current-induced effective
magnetic fields in the ferromagnetic semiconductors (Ga,Mn)As and (Ga,Mn)(As,P).
These current-induced fields have their origin in the spin-orbit interaction [2-4]. Effective magnetic fields are observed with
symmetries which resemble the Dresselhaus and Rashba spin-orbit interactions and which depend on the diagonal and off-diagonal
strain respectively. Ferromagnetic semiconductor materials of different strains, annealing conditions and concentrations are
studied and the results compared with theoretical calculations.
Our original study measured the rectification voltage coming from the product of the oscillatory magnetoresistance, during
magnetization precession, and the alternating current. More recently we have developed an impedance matching technique which
enables us to extract microwave voltages from these high resistance (10 kΩ) samples [5]. In this way we measure the microwave
voltage coming from the product of the oscillating magneto-resistance and a direct current. The applied direct current is observed
to affect the amplitude and phase of magnetization precession, indicating that anti-damping as well as field-like torques
could be present.
[1] D. Fang et al. Nat. Nano. 6, 413 (2011).
[2] A. Chernyshov et al. Nat. Phys. 5, 656 (2009).
[3] A. Manchon and S. Zhang Phys. Rev. B 79, 094422 (2009).
[4] I. Garate and A. H. MacDonald Phys. Rev. B 80, 134403 (2009).
[5] D. Fang et al. Appl. Phys. Lett. 101, 182402 (2012).
31

Spin torques induced by spin-orbit
coupling in ferromagnetic
semiconductors
Hang Li, Xuhui Wang, Fatih Dogan and Aurelien Manchon
King Abdullah University of Science and Technology, Physical Science and Engineering Division, Thuwal, Saudi Arabia
The manipulation and control of magnetization is an important topic due to its potential application for spintronic devices
such as high density magnetic Memories.[1] Through spin transfer torque, spin polarized current acting on the localized
spin in ferromagnet leads to a magnetization switching. Beside the spin transfer torque, the spin orbit torque in
ferromagnetic semiconductor has been studied both by theory and experiment.[2,3] In contrast with spin transfer torque,
the spin-orbit torque transfer the orbital angular momentum of carriers to the spin angular momentum of the local
magnetization. The spin orbit coupling acts as an “effective magnetic field” and generates a nonequilibrium spin density
that exert a torque on the magnetization.[2]
Several experiments on magnetization switching in (Ga,Mn)As have provided strong indication on the spin torque induced
by a Dresselhaus-type spin-orbit coupling, achieving critical switching currents as low as 106 A/cm2. The role of current,
electric field and temperature has been studied. [3]
The present study addresses the nature of SOC-torque in DMS in the framework of Luttinger Hamiltonian (GaMnAs,
InMnAs, etc.). Based on kinetic-exchange model, the non-equilibrium spin transport in DMS is studied theoretically within
the first-order Born approximation. Linear Dresselhaus SOC is examined and the angular dependence and magnitude of the
SOC-torque are studied for a wide range of parameters. The role of the carrier concentration and shape of the Fermi
surface are emphasized and experimental implications are discussed.
[1] D. C. Ralph and M. D. Stile, J. Magn. Magn. Mat. 320 1190 (2008)
[2] A. Manchon and S. Zhang, Phys. Rev. B 78, 212405 (2008); A. Manchon and S. Zhang, ibid, 79, 094422 (2009)
[3] A. Chernyshov, M. Overby, X. Liu, J. K. Furdyna, Y. Lyanda-Geller, and L. P. Rokhinson, Nature Phys. 5, 656 (2009). M. Endo, F.
Matsukura, and H. Ohno, Appl. Phys. Lett. 97, 222501 (2010). D. Fang, H. Kurebayashi, J. Wunderlich, K. Vyborny, L. P. Zarbo, R.
P. Campion, A. Casiraghi, B. L. Gallagher, T. Jungwirth, and A. J. Ferguson, Nature Nanotech. 6, 413 (2011).
32

Surface state driven spin-torque
in topological-insulator/
ferromagnetic-metal bilayers
Mark Fischer 1* , Abolhassan Vaezi 1 , Aurelien Manchon 2 , Eun-Ah Kim 1
1 Department of Physics, Cornell University, US
2 Materials Science and Engineering, KAUST, Saudi Arabia
‎*email of presenting author:mark.fischer@cornell.edu
We would like to present our latest findings on topological-insulator-surface-state driven spin-torque[1]. A hallmark of surface
states in strong three-dimensional topological insulators (TI) is the helical spin texture. While there have been proposals on
exploiting this spin texture for spintronics applications, they focused on TI / ferromagnetic-insulator (FI) structures predicting
field-like torque due to spin accumulation. Motivated by recent spin-torque experiments on Pt / ferromagnetic-metal(FM)
structures, we consider a TI / FM bilayer, where the ferromagnetic polarization as well as the current driven through the system
are in plane. While in general topological insulators have a conducting bulk, recent transport experiments showed that the main
contribution to the current in thin films comes from two distinct surface states: the topological Dirac surface state and an
additional two-dimensional electron gas with Rashba spin-orbit coupling. Based on this, we consider spin torque in the TI-FI
structure due to the two surface states. We find that each surface state leads to out-of-plane (field-like) torque due to spin
accumulation in the presence of a current. Moreover, we find an in-plane torque due to spin diffusion into the FM, an effect absent
in TI / FI structures. Interestingly, the two surface states contribute with opposite sign to the spin density. This allows for the
experimental identification of the dominant source of spin torque based on its sign.
[1] Mark Fischer et al, Surface state driven spin-torque in topological-insulator/ferromagnetic-metal bilayers,
in preparation (2013).
33

Angular dependence of
spin-orbit spin transfer torque
Kyung-Jin Lee 1 *, M. D. Stiles 2 , and P. M. Haney 2
1 Department of Materials Science and Engineering, Korea University, Korea
2 Center for Nanoscale Science and Technology, National Institute of Standards and Technology, US
‎*email of presenting author: kj_lee@korea.ac.kr
Magnetocrystalline anisotropy arises from the modification of electron states by spin-orbit coupling and is determined by
integrating over all occupied electron states. On the other hand, current-induced spin transfer torques arise from the changes in
torques that arise from changes in electron populations in the presence of a current. In this respect, spin transfer torques caused
by spin-orbit coupling can be interpreted as current-induced corrections to the magnetic anisotropy. From this perspective, we
expect a close relationship between the magnetic anisotropy and spin-orbit spin torques. We theoretically study this relationship
between magnetic anisotropy and spin-orbit spin torque for a ferromagnet subject to Rashba spin-orbit coupling. For a
two-dimensional free-electron model, we find that Rashba spin-orbit coupling results in perpendicular magnetic anisotropy and
field-like current-induced spin transfer torques. Both quantities acquire nontrivial angular dependence as the spin-orbit coupling
becomes comparable to the s-d exchange interaction. This nontrivial angular dependence can be understood from Fermi surface
distortion. In the limits where either the spin-orbit coupling or the s-d exchange interaction is much greater than the other, the
Fermi surface consists of two concentric circles, but when they are comparable it distorts. These free-electron calculations are in
qualitative agreement with ab initio calculations for Co|Pt bilayers, suggesting that the spin-orbit coupling at the interface is
non-negligible in comparison to the s-d exchange interaction there. The nontrivial angular dependence of spin-orbit spin torque
may be used as an indicator of strong interfacial spin-orbit coupling, because the spin-orbit spin torque that is induced by the spin
Hall effect, has a simple sinθ dependence where θ is the angle between the magnetization and the spin injected into a ferromagnet.
34

Designing Rashba
spin torque devices
Christian Ortiz Pauyac 1 , Xuhui Wang 1 , and Aurelien Manchon 1
1 King Abdullah University of Science and Technology, Physical Science and Engineering Division, Thuwal, Saudi Arabia
In an ultrathin ferromagnetic film, the interplay between a Rashba spin-orbit coupling and an exchange field gives rise to a Rashba
spin torque. Using Keldysh technique, in the presence of both magnetism and spin-orbit coupling, we derive a spin diffusion
equation that provides a coherent description to the diffusive spin dynamics in a realistic device element. We investigate first the
diffusive Rashba spin torque - and the spin density - in two regimes (weak and strong Rashba couplings) when the Rashba induced
field is perpendicular to the exchange field, as well as the transition between both regimes.
Second, we focus on the Rashba spin torque as a function of magnetization orientation. In the first case we find that the spin
torque consists of two components, originally called in-plane and out-of-plane spin torques, the first- (second-) one decreases
(increases) as we move from the weak Rashba to strong Rashba regime. In the second case the impact of diffusion reveal the
existence of a non-vanishing torque even when the magnetization and effective Rashba field are aligned. This allows us to
reconsider the spin torque components in spherical basis and we find that they oscillate as the magnetization direction changes
and such oscillation phases out as the device size increases in the weak Rashba regime, whereas it remains sizable in the strong
Rashba regime. These findings are in agreement with very recent experiments.
35

Spin-orbit Torques in
Ferromagnetic Thin Films
I. M. Miron 1 , K. Garello 2 , E. Jué1, G. Gaudin 1 , P.-J. Zermatten 1 , M. V. Costache 2 ,
S. Auffret 1 , S. Bandiera 1 , B. Rodmacq 1 , J. Vogel 5 , S. Pizzini 5 , A. Schuhl 5 ,
and P. Gambardella 2,3,4
1 SPINTEC, UMR-8191, CEA/CNRS/UJF/GINP, INAC, Grenoble, France
2 Catalan Institute of Nanotechnology (ICN-CIN2), Barcelona, Spain
3 Departament de Física, Universitat Autonoma de Barcelona (UAB), Barcelona, Spain
4 Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
5 Néel Institute CNRS Grenoble, France
Materials with large coercivity and perpendicular magnetic anisotropy represent the mainstay data storage media, thanks to their
ability to retain a stable magnetization state over long periods of time and their compliance with increasing miniaturization steps.
A major concern is that the same anisotropy properties that make a material attractive for storage also make it hard to write.
We address this issue by investigating novel spin torque mechanisms based on spin-orbit effects. It is well known that spin-orbit
coupling is ultimately responsible for magnetocrystalline anisotropy and damping. Under certain conditions, however, spin-orbit
effects might either induce [1,2,3] or enhance [4,5] specific spin torque mechanisms.
We show that in materials lacking inversion symmetry, the spin accumulation induced by the current creates torques on the
magnetization. We analyze the expected symmetry of these torques in uniformly magnetized layers as well as magnetic domain
walls, and evidence experimentally their existence in agreement with symmetry arguments.
[1] A. Manchon and S. Zhang, PRB 78 212405 (2008).
[2] I.M. Miron et al. Nature Materials 9, 230-234 (2010)
[3] I.M. Miron et al. Nature 476, 189-193 (2011)
[4] I.M. Miron et al. PRL 102, 137202 (2009)
[5] I.M. Miron et al. Nature Materials 10, 419 (2011).
36

Scattering theory of
current-induced
magnetization dynamics
Kjetil M. D. Hals 1 *, Arne Brataas 1 , Yaroslav Tserkovnyak 2
1 Department of Physics, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway
2 Department of Physics and Astronomy, University of California, Los Angeles, California 900095, US
‎*email of presenting author: kjetil.hals@ntnu.no
When a spin-polarized current traverses a ferromagnet, the spin-current component perpendicular to the magnetization direction
is absorbed by the magnetic system. The absorbed angular momentum yields a spin-transfer torque (STT) on the magnetization. In
systems where spin-orbit coupling breaks the spatial inversion symmetry, there is also a charge-current torque (CCT). The STT and
CCT effects are respectively the reciprocal effects to spin-pumping and charge-pumping by a precessing magnetization. Onsager
reciprocal relations relate the response coefficients for a process and its reciprocal process. We explain how one can use Onsager
reciprocal relations to formulate a scattering theory of spin- and charge- current induced magnetization dynamics [1]. As an
application of the formalism, we study the CCT effect in a dirty, layered GaAs|(Ga,Mn)As|GaAs system and find magnetization
switching for current-densities as low as 5*10^6 A/cm^2 [1].
[1] Kjetil M. D. Hals, Arne Brataas, Yaroslav Tserkovnyak, Scattering Theory of Charge-Current Induced Magnetization Dynamics,
Europhysics Letters 90, 47002 (2010).
37

Spin-Hall nano-oscillators
S. O. Demokritov 1 , H. Ulrichs 1 , V. E. Demidov 1 , S. Urazhdin 2 , V. Tiberkevich 3 , A. Slavin 3
1 University of Muenster, Corrensstrasse 2-4, 48149 Muenster, Germany
2 Emory University, Atlanta, GA 30322, US
3 Department of Physics, Oakland University, Rochester, MI, US
The interplay between spin transport and magnetization, a collective property of the electrons, plays a central role in spin-based
electronic devices. The effect of spin current on the magnetic configuration results from the modification of the dynamical
properties of nanomagnets by the spin transfer torque (STT). In particular, STT changes the effective magnetic damping.
We use micro-focus Brillouin light scattering spectroscopy to study magnetic fluctuations in a Permalloy microdisc located on top
of a Pt strip carrying an electric current. Magnetic dynamics in our nano-devices is driven by pure spin currents generated due to
the spin Hall effect in the Pt electrode. We show that the fluctuations can be efficiently suppressed or enhanced by different
directions of the electric current. Additionally, we find that the effect of spin current on magnetic fluctuations is strongly
influenced by nonlinear magnon-magnon interactions, which prohibit auto-generation in this geometry [1].
Using a local injection of spin current by Pt into an extended Permalloy film and taking advantage of the radiational losses of spin
waves, we demonstrate that above a certain current threshold, our device enters a single-mode coherent auto-oscillation regime
with the frequency of oscillation 5-10 GHz [2]. The corresponding strongly-localized dynamic mode with the diameter below100
nanometers, has characteristics reminiscent of the nonlinear stationary spin-wave “bullet”[3]. Similar to conventional spin-torque
nano-oscillators (STNO) the realized spin-Hall-effect nano-oscillator reperesents a tuneable microwave generator with a linewidth
of about 10 MHz. Moreover, we show that it can be synchronized to the external microwave signal.
Our findings suggest a route for the implementation of novel magnetic nano-oscillators that have significant advantages over
STNOs, whose geometry and structure are limited by the requirement that the spin current is accompanied by the electric current
flowing through the ferromagnet.
[1] Demidov et al. Phys. Rev. Lett. 107, 107204 (2011).
[2] Demidov et al. Nature Materials 11, 1028 (2012).
[3] Slavin, A. & V. Tiberkevich, Phys. Rev. Lett. 95, 237201 (2005).
38

Poster Presentations
39

Quantum spin hall effect,
valley hall effect, and
topological insulator phase
transitions in silicone
M. Tahir*, A. Manchon, and U. Schwingenschlogl
King Abdullah University of Science and Technology, Physical Science and Engineering Division, Thuwal, Saudi Arabia‎
*email of presenting author: Muhammad.tahir@kaust.edu.sa
We demonstrate theoretically the realization of quantum spin and quantum valley Hall effects in silicene [1]. We show that
combination of electric field and intrinsic spin-orbit interaction leads to quantum phase transitions from a two dimensional
topological insulator to a trivial insulating state. They are accompanied by a quenching of the quantum spin Hall effect and the
onset of a valley Hall effect, providing a tool to experimentally tune the topological state of silicene. In contrast to graphene and
other conventional topological insulators, the proposed effects in silicene are accessible to experiments.
[1] M. Tahir, A. Manchon, K. Sabeeh, and U. Schwingenschlogl, arXiv:1206.3650.
40

Interplay of magnetization
dynamics and pure spin currents
Henning Ulrichs, V. E. Demidov, S. O. Demokritov
University of Muenster, Corrensstrasse 2-4, 48149 Muenster, Germany
S. Urazhdin
Emory University, Atlanta, GA 30322, US
In high-frequency spintronic devices, spin transfer torque (STT) phenomena
allow to enrich conventional electronics with functionalities based on
dynamic magnetization. In this poster we present in detail our recent
experimental studies [1-4] on the subject, done by micro-focus Brillouin light
scattering spectroscopy (BLS). BLS allows frequency-, spatial-, and timeresolved
measurements of dynamic magnetization, providing the most
complete picture experimentally available.
In the first series of experiments [1-3] we investigated Permalloy (Py)
microdiscs on top of a Pt strip, which serves as a conductor for dc electric
current. Due to the Spin-Hall effect in the Pt electrode, a transverse spin
current is generated and exerts a spin transfer torque on the adjacent Py disc.
Studying the effect of pure spin currents on thermal magnetic fluctuations,
we show that they can be controllably enhanced or suppressed [1] (see Figure 1a).
The Pt electrode can also carry microwave currents, whose dynamic magnetic
field drives the Py disc into Ferromagnetic Resonance (FMR). We demonstrate
that when adding dc currents in this situation, the resulting STT can be
utilized for a wide-range control of the effective magnetic damping [2].
Depending on the sign of the current flow, damping is either increased or
decreased, deviating significantly from the value at zero current (see Figure
2a). For practical application this effect can be utilized for creation of tunable
microwave-filters combining a narrow line width with a high agility.
STT caused by spin current can also be used for stimulation and electric
control of nonlinear dynamic phenomena such as parametric spin-wave
instability. For this we applied microwave currents at twice the FMR
frequency. Without the help of the spin currents, the threshold of the
parametric pumping caused by the natural damping is too high. However, by
means of the pure spin current, the effective damping and as a consequence
the threshold can be controllably shifted down, so that the parametric
instability can be observed [3] (see Figure 2b).
Fig. 1 (a) Enhancement and suppression of thermal magnetic
fluctuations in a device with non-local injection of the spin
current (b) Transition to auto-oscillation regime via formation of
a new self-localized “bullet” mode in a device with local spincurrent
injection. Inset shows a measured spatial map of the
self-localized mode. For illustration purposes, one quarter of the
structure is left out in the schematics. Red arrows indicate the
current flow.
Fig. 2 (a) Wide-range control of the effective Gilbert damping
parameter by pure spin current in a layered system Py/Cu/Pt. (b)
Stimulation of the parametric spin-wave instability and control of
its threshold power by pure spin current.
In the device geometry considered so far, the spin current was injected into Py uniformly. In this case, we found that interaction of
the auto-oscillating mode with short-wavelength spin-wave modes inhibits the onset of auto-oscillations.
To overcome this problem, we utilized a spatially confined spin current injection using a special design of the electrodes (see Figure
1b) [4]. Here, the electric current flows through the Pt layer in the gap between the electrodes. As a result the spin current and
the corresponding STT acts on Py only locally. Short-wavelength spin wave modes now suffer from radiation losses, and therefore
cannot suppress the auto-oscillations, which now appear when the current exceeds a certain threshold. We have found
experimentally, that the corresponding mode has spatial dimensions below 100 nanometers, is highly coherent (line width about
10 MHz), and tunable in frequency (5-10 GHz) by means of the external magnetic field.
While the basic features of this device resemble conventional spin-torque nano-oscillators, it has the practical advantage, that no
transverse flow of real electric current through the ferromagnet is necessary. Furthermore, the all planar geometry allows optical
access to the active area, enabling direct study of the physics of STT phenomena.
[1] Demidov et al. Phys. Rev. Lett. 107, 107204 (2011).
[2] Demidov et al. Appl. Phys. Lett. 99, 172501 (2011).
[3] Edwards et al. Phys. Rev. B 86, 134420 (2012).
[4] Demidov et al. Nature Materials 11, 1028 (2012).
41

Current-induced domain-walls
motion in presence of spin-orbit
torque in Pt/Co/AlOx trilayers
E. Jue
SPINTEC, UMR-8191, CEA/CNRS/UJF/GINP, INAC, F-38054 Grenoble, France
Current-induced domain-wall (CIDW) motion through the spin-transfer
torque (STT) has attracted a lot of attention in recent years. Besides its
potential applications to magnetic data storage this mechanism shows a
wealth of remarkable physical phenomena.
CIDW motion in structures of inversion asymmetry (SIA) like Pt/Co/AlOx
trilayers has shown to be much more complex than a standard description
involving only the adiabatic and non-adiabatic terms (NA) of the STT. The
enhancement of the spin-orbit (SO) interaction due to the SIA results for
example in a large increase of the STT efficiency [1] and gives rise to a
transverse effective magnetic field Heff resulting from both the Rashba effect
and the s-d exchange interaction [2]. These two effects modify considerably
the DW dynamics: the high mobility regime generated by the large NA term
is extended to high current density by the stabilizing effect of Heff which
prevents the DW transformations [3].
Fig. 1 DW mobility as a function of a transverse magnetic field.
This description is still incomplete since it does not take into account the
influence of a strong spin orbit torque (SOT) whose existence has been
experimentally demonstrated recently [4,5]. Due to its symmetry, this SOT acts
as an effective field oriented along the easy axis for the magnetization inside
the DW. Thus, its influence can not be easily distinguished from that of the NA
torque in simple velocity measurements.
In this presentation, we show that the SOT modifies qualitatively and
quantitatively the DW dynamics. In order to highlight its effect, we studied the
DW motion induced by a current in the presence of a transverse magnetic field
HT in Pt/Co/AlOx wires.
Instead of observing two distinct regimes of mobility as we could expect
considering that HT simply competes with Heff, we observe a continuous
change of the DW velocity with HT. Moreover the DW mobility increases
linearly with HT (fig 1). We explain our results taking into account STT as well
as Heff and SOT.
Besides the possibility of modulating continuously the DW mobility, our results
highlight the important role of the SO interaction on DW dynamics.
[1] I. M. Miron et al., Phys. Rev. Lett. 102, 137202 (2009).
[2] I. M. Miron et al., Nature Materials, 9, 230–234 (2010).
[3] I. M. Miron et al., Nature Materials, 10, 419–423 (2011).
[4] I. M. Miron et al., Nature 476, 189 (2011).
[5] L. Liu et al., Science 336, 555 (2012).
42

Ge-intercalated graphene:
The origin of the p-type to
n-type transition
U. Schwingenschlögl, T. P. Kaloni*
King Abdullah University of Science and Technology, Physical Science and Engineering Division, Thuwal, Saudi Arabia
‎*email of presenting author: thaneshwor.kaloni@kaust.edu.sa
We would like to present our latest findings on Ge-intercalated graphene on SiC(0001) [1]. Recently huge interest has been
focussed on Ge-intercalated grapheme [2]. In order to address the effect of Ge on the electronic structure, we study Ge-intercalated
free-standing C 6 and C 8 bilayer graphene, bulk C 6 Ge and C 8 Ge, as well as Ge-intercalated graphene on a SiC(0001) substrate, by
density functional theory. In the presence of SiC(0001), there are three ways to obtain n-type graphene: i) intercalation between
C layers; ii) intercalation at the interface to the substrate in combination with Ge deposition on the surface; and iii) cluster
intercalation. All other configurations under study result in p-type states irrespective of the Ge coverage. We explain the origin of
the different doping states and establish the conditions under which a transition occurs.
[1] T. P. Kaloni et al. EPL 99, 57002 (2012).
[2] V. Emtsev et al. Phys. Rev. B 84, 125423 (2011).
43

Enhancement of spin-pumping
signal by Cu interlayer
Praveen Deorani, K. Narayanapillai, C. S. Bhatia, and Hyunsoo Yang
Department of Electrical and Computer Engineering, National University of Singapore, Singapore
Spin-pumping [1-3] refers to the generation of pure spin currents by a precessing magnetization in a ferromagnet (F). The
generated spin current is transferred to the adjacent nonmagnet (N) at the F/N interface and is commonly measured as a dc
voltage induced by the inverse spin Hall effect (ISHE) [3-4] in N. The efficiency of spin-pumping is given by the spin mixing
conductance [1], which depends on N and the F/N interface. Inserting a metallic layer at the interface can change the efficiency
of spin-pumping and is potentially useful for increasing the induced spin current.
We report study of spin-pumping through a Cu layer inserted at the permalloy (20 nm)/ Ta (8 nm) interface. Different devices with
the Cu thickness ranging from 0.2 to 5 nm have been studied. The magnetization dynamics in the Py is generated by a micorwave
magnetic field, and the resultant ISHE signal is measured across Ta as a function of magnetic field. An enhancement in the ISHE
signal up to 2 times induced by spin-pumping is observed in the presence of the Cu interlayer. The enhancement can be attributed
to increase in efficiency of spin-pumping from Py or in spin Hall effect in (Cu)/Ta. In order to confirm this, ferromagnetic resonance
(FMR) measurements have been done on Py/Cu/Ta films to observe changes in Gilbert damping constant (α ) due to spin pumping.
[1] Y. Tserknovnyak, A. Brataas, and G. E. W. Bauer, Phys. Rev. B 66, 224403 (2002).
[2] K. Ando et al., Phys. Rev. B 78, 014413 (2008).
[3] E. Saitoh et al., Appl. Phys. Lett. 88, 182509 (2006).
[4] S. O. Valenzuela and M. Tinkham, Nature 442, 176 (2006).
.
44

Effective Chiral Ordering Induced
by Rashba Interaction
Kyoung-Whan Kim 1 , Kyung-Jin Lee 2 , and Hyun-Woo Lee 1
1 PCTP and Department of Physics, Pohang University of Science and Technology, Kyungbuk 790-783, Korea
2 Department of Materials Science and Engineering, Korea University, Seoul 136-701, Korea
A Ferromagnetic system prefers magnetization structure which minimizes total effective magnetic energy. In this work we show
that the energy of conduction electron is also affected by magnetic structure. Therefore, the system tends to minimize not only
magnetic energy but the sum of magnetic energy and conduction electron energy. Consequently, considering conduction electron
energy is crucial for determining stable magnetic configuration and studying magnetization dynamics such as domain wall motion.
As a specific case, we study Rashba spin-orbit coupling system and show that the Rashba interaction may give rise to chiral
ordering of magnetization. Our work is expected to be helpful to explain anomalous phenomena of magnetization dynamics in thin
film structures and also implies that the Rashba interaction may have similar effects as Dzyaloshinskii-Moriya interaction.
45

Angular dependence of
current-induced field-like
spin transfer torque in
Pt|Co|MgO structures
Ki-Seung Lee 1, 2* , Byung-Chul Min 2 , Seo-Won Lee 1 , Kyung-Ho Shin 2
and Kyung-Jin Lee 1,2
1 Department of Materials Science and Engineering, Korea University, Seoul 136-701, Korea
2 Spin Convergence Research Center, Korea Institute of Science Technology, Seoul, 136-791, Korea
‎*email of presenting author: kslee77@kist.re.kr
Manipulation of local magnetization using electrical current has attracted considerable interest due to its rich physics and
applications for a new class of spintronic devices. It was theoretically proposed that spin transfer torque caused by Rashba spinorbit
coupling yields a new type of current-induced effective magnetic field [1], i.e. Rashba magnetic field. The existence of this
Rashba field in the structure consisting of non-magnetic metal | ferromagnetic metal | oxide was reported experimentally [2]. In
this work, we investigate the angular dependence of current-induced field-like spin transfer torque in Pt (2nm)|Co(0.6nm)|MgO(2nm)
using lock-in technique [3]. We find that current-induced field-like spin transfer torque depends strongly on the magnetization
direction. This non-trivial angular dependence is qualitatively consistent with a recent theoretical prediction [4] based on the
assumption that the Rashba spin-orbit coupling is comparable to the s-d exchange coupling. Our result suggests that the interfacial
spin-orbit coupling in such structures is strong enough to modify the angular dependence of spin-orbit-related spin transfer torque.
[1] K. Obata and G. Tatara, Phys. Rev. B 77, 214429 (2008) ; A. Manchon and S. Zhang, Phy. Rev. B 78, 212405 (2008).
[2] I. M. Miron et al., Nature Mater. 9, 230 (2010).
[3] U. H. Pi et al., Appl . Phys. Lett. 97, 162507 (2010).
[4] K.-J. Lee, H.-W. Lee, A. Manchon, P. M. Haney, and M. D. Stiles, unpublished.
46

Current-Induced Domain Wall
Depinning With A Spin Hall Effect
Jisu Ryu 1 , Kyung-Jin Lee 2 , Hyun-Woo Lee 1
1 PCTP and Department of Physics, Pohang University of Science and Technology, Kyungbuk 790-783, Korea
2 Department of Materials Science and Engineering, Korea University, Seoul 136-701, Korea
Recently, a spin Hall effect-induced magnetization reversal is observed [1]
and attracted great attention for its potential as low-power-consuming
switching device applications. A magnetic domain wall (DW) motion with a
spin Hall effect in ideal nanowires, where extrinsic pinning potentials are
absent, is studied in Ref. [2].
In practical situations, however, DW dynamics can be largely affected by
extrinsic pinning potentials due to edge roughness and defects of nanowires
[3]. Here, we study DW motion with a spin Hall effect in the presence of an
extrinsic pinning potential. We first calculate a threshold current density JC,
the minimum current density value needed to depin a DW from an extrinsic
pinning potential. Figure shows JC as a function of the pinning potential
depth V for two different DW chiralities (ф0 = 0° or 180°) and for various spin
Hall effect strengths (BSHλ). JC slightly increases for the one DW chirality
but significantly decreases for the other DW chirality. By analyzing dynamics
of two DW collective coordinates, we found the JC reduction originates from
the negative damping ratio of a DW oscillation inside the pinning potential
due to the spin Hall effect. Recent theoretical study [2] reported that in ideal
nanowires, the spin Hall effect may drive a DW with certain
chirality against electron flow direction in a particular current density range.
We secondly check how extrinsic pinning potentials affect this reversed DW
motion. For a reasonable parameter set, we estimate that V should be smaller
than 4% of the DW hard-axis anisotropy energy for the current range of the
reversed DW motion to avoid getting masked by JC. In summary, we
investigated current-driven DW motion with a spin Hall effect in the presence
of extrinsic pinning potentials. We found that a spin Hall effect may
significantly reduce JC and we also provide an estimation of V for the
observation of the reversed DW motion.
[1] L. Liu et al., arXiv: 1110.6846v2 (2011); L. Liu et al., Science 336, 555(2012).
[2] S.-M. Seo et al., Appl. Phys. Lett. 101, 022405(2012).
[3] G. Tatara et al., Phys. Rev. Lett. 92, 086601(2004).
47

Role of tunneling characteristics
on the performance of
Stt--‐Mram tunnel junctions
Jimmy J. Kan 1 , Kangho Lee 2 , Matthias Gottwald 1 , Seung H. Kang 2 ,
and Eric E. Fullerton 1
1 Center for Magnetic Recording Research, UCSD, L Jolla, CA, US
2 Advanced Technology, Qualcomm Incorporated, San Diego, CA, US
Second generation Magnetic Random Access Memory (MRAM) driven by the Spin Transfer Torque (STT) switching is emerging as
a competitive candidate in the field of new solid‐state memories STT ‐MRAM promises reduced power, higher density, and better
CMOS integration compared to first generation MRAM driven by magnetic field. These characteristics make STT‐MRAM an
excellent candidate for both embedded and standalone memory applications [1].
The operational element of STT‐MRAM is the magnetic tunnel junction (MTJ): a spintronic structure consisting of a ferromagnetic
reference layer, an ultrathin MgO dielectric tunneling barrier, and a ferromagnetic free layer. By passing bipolar current through
the MTJ, this memory element can be set into a parallel (P, low-resistance) or anti-parallel (AP, high-resistance) state.
One important technological challenge for STT-MRAM that is often neglected because of a large emphasis on write-power and
thermal stability [2] is the so‐called “IC asymmetry” of MTJ cells. The mean and deviation of the programming current pulse at all
pulse widths demonstrates an asymmetry dependent on the switching direction of the MTJ. Typically, the P‐to‐AP switching
current or latency is higher than AP-to-P writing due to a difference in AP4 P and P4 AP spin---torque efficiency parameters (η).
This problem causes MTJs to be incompatible with standard NMOS driving transistors, which have their own current driving
asymmetry depending on polarity of operation. MTJ switching is also a thermally-driven probabilistic process [3], so the IC
asymmetry problem also introduces persistent switching errors that negatively impact the device’s write- error rate (WER) falloff
slope, severely impacting the write reliability.
In this work, we report on the performance of in-plane MTJ devices with a particular focus on the origins of asymmetric write-error
rates (WER) [4]. We compare the magnetic properties of two classes of similar in-plane MTJs that show significantly different read
disturb rate (RDR) (Fig.1) and WER characteristics and find that improving factors such as damping parameter, thermal stability
parameter, and average switching voltages/currents do not necessarily lead to an improvement in WER falloff (Fig. 2). Through
magnetometry, ferromagnetic resonance and temperature-dependent magneto‐transport measurements of MTJs Including
low-temperature state diagrams, we demonstrate that WER slopes and IC asymmetry are correlated to intrinsic material properties
of MTJs such as TMR, spin‐torque efficiency and spin‐polarization (Fig.3) and are not dominated by thermal effects as previously
assumed. We further show that low‐temperature measurements can elucidate anomalous device properties that lead to failures
in room‐temperature STT‐MRAM operation.
[1] K. Lee, et al. IEEE Trans. Mag., 47, pp. 131---136 (2010)
[2] T. Seki, et al. Appl. Phys. Lett. 99, 112504 (2011)
[3] E.B. Myers, et al. Phys. Rev. Lett. 89, 196801 (2002)
[4] K. Lee, et al. IEEE Mag. Lett. (accepted 2012)
48

Theory of ultrafast non-thermal
spin dynamics
Hasan Kesserwan 1 , Fatih Dogan 1 , Aurelien Manchon 1
1 King Abdullah University of Science and Technology, Physical Science and Engineering Division, Thuwal, Saudi Arabia
Manipulating the order parameter of magnetic materials on ultrashort timescales has been made possible by the use of femtosecond
laser excitations [1]. Ultrafast demagnetization and magnetization dynamics has been observed in ferro-, ferri- and even
anti-ferromagnets [2, 3]. However, the popular three-temperature model widely used to interpret the experiments fails to capture
the core of non-thermal physics taking place during the first hundreds of femtoseconds. Recent experiments identified the spin
orbit interaction [4] and the magnon excitations [5] as possible candidates responsible for the dissipation of the spin angular
momentum and consequently for the ultrafast demagnetization. However, the interplay between these two mechanisms has not
been clearly identified. Theoretically, several models have been proposed to understand the ultrafast phenomenon, for example
Zhang and Hubner [6], U. Atxitia et al. [7] and recently the three temperature model proposed by Manchon et al. [8].
In the present work, we develop a non-equilibrium description of the charge, spin and phonon dynamics using the microscopic
Kinetic Bloch Spin Equation (KSBE) [9] that governs the dynamics of the three mutually coupled subsystems. The KSBE incorporates
all the pertinent scattering mechanisms that could demagnetize the magnetic material, such as the electron-electron,
electron-impurities, electron-phonon, and electron-magnon. We show that on ultra-short time scales, the light-induced ultrafast
demagnetization is due to an Elliott-Yafet Spin flip mechanism mediated by electron-electron, electron-phonon or impurity
scattering. Our perspective is to analyse the interplay between Elliott-Yafet processes, mediated by electron-electron,
electron-phonon and electron-impurities, and electron-magnon scattering. The strength of the present code, compared to previous
approaches, is that it can in principle track the non-thermal distribution of electrons, magnons and phonons and provides a full
dynamical picture of the ultrafast dynamics.
[1] E. Beaurepaire et al., Phys. Rev. Lett. 76, 4250 (1996).
[2] B. Koopmans et al., Nature Materials 9, 259 (2010).
[3] I. Radu et al., Nature 472, 205 (2011).
[4] C. Boeglin et al., Nature 465, 458 (2010).
[5] A. B. Schmidt et al., Phys. Rev. Lett. 105, 197401 (2010).
[6] G. Zhang, Phys. Rev. Lett. 85, 3025 (2000).
[7] U. Atxitia, Phys. Rev. B 81, 174401 (2010).
[8] A. Manchon et al. , Phys. Rev. B 85, 064408 (2012)
[9] J. H. Jiang et al., Phys. Rev. B 79, 125206 (2009).
49

Anomalous Hall effect (AHE) and
anisotropy magnetoresistance
(AMR) in perpendicularly
magnetized Co/Ni multilayers
See-Hun Yang1*, Priscila Barba2, Kwang-su Ryu1, Luc Thomas1,
Aurelien Manchon2, and Stuart Parkin1
1IBM Almaden Research Center, US
2 King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
‎*email of presenting author: seeyang@us.ibm.com
Unconventional current-induced domain wall motion (CIDWM) faster than 300 m/s along the current direction has been reported
in perpendicularly magnetized atomically thin Co/Ni bilayers deposited on Pt underlayers [1], making these materials extremely
promising for DW-based memory and logic devices. The driving force of the motion is believed to originate from the Pt/Co
interface. Indeed, we find that when Pt is replaced by Au, a closely related 5d metal, CIDWM is conventional, namely the DWs
move against the current flow, and several times more slowly. We have compared the anomalous Hall effect (AHE) and anisotropic
magnetoresistance (AMR) of Co/Ni multilayers on Pt and Au underlayers. We find that the orientation dependence of the AMR is
very different in the two cases and the AHE is more than an order of magnitude greater for Pt/Co/Ni than for Au/Co/Ni. We discuss
the origin of these behaviors.
[1] Kwang-su Ryu, Luc Thomas, See-Hun Yang, S.S.P. Parkin, Applied Physics Express 5, 093006 (2012).
50

Direct Connection between Spin
Torque and Anomalous Transport
induced by Spin Hall Effect
Priscila Barba , See-Hun Yang , Luc Thomas 2 , Kwang-Su Ryu 2 , Stuart Parkin 2
and Aurelien Manchon 1
1 King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
2 IBM Almaden Research Center, San Jose, CA, US
Spin-orbit-induced anisotropic transport in magnetic materials has recently experienced a renewed interest thanks to the
formulation of anisotropic spin scattering in terms of Berry’s curvature. Anisotropic magnetoresistance (AMR) is related to the
scattering of the transport electrons on the orbitals of localized electrons, depending on the magnetization direction. The
contribution of the interfaces on AMR has been only scarcely studied. We consider a bilayer composed of a ferromagnetic layer
adjacent to a normal metal. The normal metal displays spin Hall effect, whereas the ferromagnetic layer possesses anomalous Hall
effect (AHE). We propose that spin Hall effect present in the bottom layers might contribute to the total AMR and AHE of the
bilayer system. The charge and spin currents are analyzed by drift-diffusion equations including the role of inverse spin Hall effect
as well as anomalous Hall effect in the ferromagnet. Longitudinal and transverse spin accumulations at the interfaces are captured
through spin dependent conductance and the mixing conductance. It is shown that the presence of a spin accumulation in the
normal metal close to the interface is transformed into a charge current through inverse spin Hall effect hence altering the
conductivity of the normal metal. Interestingly, we find that in the limit of large interfacial resistance, the AMR and AHE induced
by the spin Hall effect in the normal metal are directly related to the strength of the spin transfer torque.
51

Origin of coexistence of
superparamagnetic and
ferromagnetic behavior in
Mn doped ZnO thin films
S. Venkatesh, Abdulaziz Baras and Iman. S. Roqan*
King Abdullah University of Science and Technology, Materials Science and Engineering, Physical Sciences
and Engineering Division, Thuwal, Saudi Arabia
‎*email of corresponding author : iman.roqan@kaust.edu.sa
ZnO based Diluted magnetic semiconductors have been extensively studied
for the past two decades towards achieving room temperature ferromagnetism
and ‘P’ type conductivity in order to be used in spintronic devices. Although
plethora of research work have been rendered in the 3d transition metals
doped ZnO, the intrinsic ferromagnetic origin is still under debate. In this
work we present our findings on the Mn2at% doped ZnO doped ZnO thin
films were prepared by PLD technique on c-sapphire at 50 and 500 mTorr of
O2 ambient pressures. Both films were grown along the c-axis of the ZnO and
no trace of any secondary phase could be identified from XRD, SEM and TEM.
Room temperature magnetization shows a saturated ferromagnetic behavior,
however at 5 K it was superparamagnetic. A good agreement with the
Kaminski-Das Sarma model of polaron percolation [1] was obtained with the
temperature variation of ΔM (=MFC-MZFC). Low temperature charge
transport was governed by the Mott’s variable range of hopping mechanism
indicating, a strong localization of carriers at low T and below a critical
concentration in the vicinity of metal-insulator transition [2]. A large positive
magnetoresistance ( ~ 40 %) with an admixed negative component below 10
K was attributed to a field induced delocalization of weakly localized carriers
[2]. A coexistence of superparamagnetism and ferromagnetism is attributed
to the consequence of varying temperature dependences of localization
effect, polarons clustering and magnetic ordering of localized carriers.
Fig.1MvsH loops (a, b) and ZFC-FC magnetization (c, d) of Mn 2%
doped ZnO thin film samples, prepared at 50, 500 mTorr of Oxygen,
respectively. The inserts of panels (c) and (d) show the Kaminiski-
Das Sarma fit of ΔM (=M FC -M ZFC ) for the percolation of polarons.
[1] A. Kaminski and S. Das Sarma, Phys. Rev. Lett. 88, 247202 (2002)
[2] J. Jaroszyński et al., Phys. Rev. B 76, 045322 (2007)
52

Three terminal magnetic tunnel
junctions with CuIr channel
M. Yamanouchi 1,2 , L. Chen 1,2 , J. Kim 3 , M. Hayashi 3 , H. Sato 1 , S. Fukami 1 , S. Ikeda 1,2 ,
F. Matsukura 1,2,4 , and H. Ohno 1,2,4
1 Center for Spintronics Integrated Systems, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
2 Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira,
Aoba-ku, Sendai 980-8577, Japan.
3 National Institute for Materials Science, Tsukuba 305-0047, Japan.
4 WPI Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
Recently, in three terminal devices with magnetic tunnel junctions (MTJs) patterned onto channels composed of β-Ta [1] and β-W
[2], switching of MTJs by spin transfer torque (STT) driven by spin Hall effect (SHE) in the channels have been demonstrated. Such
three terminal MTJs attract much attention because of their potential of realizing high speed operation [3]. However, for practical
application, it is highly desirable to make the channel material more compatible with very large scale integrated circuits technology.
Here we show three terminal MTJs with the channel based on an interconnection material Cu with Ir doping (Cu:Ir), in which a
relatively large SHE has been reported [4].
A stack is deposited on a thermally oxidized Si (001) substrate by using rf magnetron sputtering at room temperature. The stack
structure is, from the substrate side, Cu 90 Ir 10 (10)/Co 20 Fe 60 B 20 (1.5)/MgO(1.7)/Co 20 Fe 60 B 20 (3)/Ru(0.8)/Co 50 Fe 50 (2.5)/Ta(5)/Ru(5) (in
nm). The stack is processed into 100 × 200 nm and 100 × 350 nm rectangular MTJs on a 1 μm wide Cu:Ir channel by electron-beam
lithography and Ar-ion milling. The long axis of the MTJ is directed orthogonal to the channel direction. The top and bottom CoFeB
layers exhibit in-plane magnetic easy axis and corresponds to the reference and recording layer, respectively. After preparing
parallel or antiparallel magnetization configuration, current pulses with various amplitudes and directions are applied. With the
application of a current density of less than 10 12 A/m 2 to the channel, current-direction-dependent switching of MTJ takes place.
The relationship between direction of the switching current and magnetization configuration is consistent with that by both of
STT driven by SHE in Cu:Ir [4] and current-induced fields orthogonal to the channel direction.
This work was supported by JSPS through FIRST program.
[1] L. Liu et al., Science 336, 555 (2012).
[2] C. Pai et al., Appl. Phys. Lett. 101, 122404 (2012).
[3] N. Sakimura et al., VLSI Cir. Tech. Dig., 2006, 108.
[4] Y. Niimi et al., Phys. Rev. Lett. 106, 126601 (2011).
53

Domain wall motion driven by
the Slonczewski-like torque
from nonmagnetic heavy-metal
underlayers
Satoru Emori 1 *, Uwe Bauer 1 , Sung-Min Ahn 1 , Eduardo Martinez 2 ,
Geoffrey S. D. Beach 1
1Department of Materials Science and Engineering, Massachusetts Institute of Technology, US
2Department of Applied Physics, University of Salamanca, Spain
‎*Email of Presenting Author: satorue@mit.edu
Recent studies have reported efficient current-driven domain wall (DW)
motion [1] and magnetization switching [2] in out-of-plane magnetized
structures consisting of an ultrathin ferromagnetic layer sandwiched by a
nonmagnetic heavy-metal underlayer and an oxide overlayer. We
experimentally relate DW dynamics to current-induced spin-orbit torques in
Ta/CoFe/MgO and Pt/CoFe/MgO. DWs are propagated by current alone, with
spin torque efficiencies exceeding 100 Oe/(1011 A/m2), along electron flow in
Ta/CoFe/MgO and against electron flow in Pt/CoFe/MgO. The polarities of the
measured Slonczewski-like torque in uniformly magnetized Ta/CoFe/MgO
and Pt/CoFe/MgO are also opposite, and the magnitudes of the torque are
sufficient to drive DWs. These observations are naturally accounted for by
the spin Hall effect in Ta and Pt. In contrast, according to the measurements
of the current-induced field-like torque, the Rashba effect cannot
be a fundamental contribution to DW motion. Combined with the
Dzyaloshinskii-Moriya interaction [3] that locks DWs into the Néel
configuration, the Slonczewski-like torque from the spin Hall effect in the
heavy-metal underlayer explains anomalously efficient DW motion, even in
the absence of an applied field or conventional spin transfer torques.
Figure: a,b Direction (a) and velocity (b) of current-driven DWs. c,d
Geometry of effective field HSL (c) and current-induced switching
(d) from Slonczewski-like torque under applied field HLong.
[1] I.M. Miron et al. Nat. Mater. 10, 419 (2011); S. Emori et al. Appl. Phys. Lett. 101, 042405 (2012).
[2] L. Liu et al. Phys. Rev. Lett. 109, 096602 (2012).
[3] A. Thiaville et al. Europhys. Lett. 100, 57002 (2012).
54

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