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Magnetismus Poster: Do., 13:00–15:30 D-P218
Magnetic x-ray and neutron studies of magnetization profiles and interface
roughness in multilayers with Heusler compounds
Andre Bergmann 1 , Johannis Grabis 1 , Miriana Vadala 1 , Alexei Nefedov 1 ,
Max Wolff 1 , Kurt Westerholt 1 , Boris Toperverg 2 , Hartmut Zabel 1
1 Insitute of Experimental Physics, Ruhr-University Bochum, D-44780 Bochum, Germany
– 2 Petersburg Nuclear Physics Institute, Gatchina, 188300 St. Petersburg, Russia
Presently Heusler-alloys are intensively investigated as ferromagnetic (FM) electrodes
in magnetic tunnel junctions [1] and as spin reservoir for spin-injection into semiconductor
heterojunctions [2]. Due to a half metallic splitting of the d-band at EF , the
spin polarization is predicted to be 100 %. The double Heusler compounds have a
composition of the type X2YZ, (X=Co,Ni; Y=Mn, Z=Si,Ge) and a L21 structure, consisting
of 4 interpenetrating fcc lattices. Only compounds with perfect LRO exhibit
the maximum FM saturation moment of 5µB/f.u. and half metallicity. Site disorder
decreases the polarization, the average µB, and the Curie temperature.
We have studied the structure and magnetism of the ferromagnetic Heusler compound
Co2MnGe in high-quality [Co2MnGe/Au]n, [Co2MnGe/V]n, and [Co2MnGe/Al2O3]n
-multilayers (ML) by hard x-ray scattering, soft x-ray resonant magnetic scattering
(XRMS), and polarized neutron reflectivity (PNR) [3]. The diffuse hard x-ray scattering
reveals that in [Co2MnGe/Au]n at the interfaces correlated roughness dominates
and interdiffusion is negligible, whereas in [Co2MnGe/V]n the roughness is uncorrelated
and dominated by interdiffusion. In [Co2MnGe/Al2O3]n ML the interfaces are
very sharp. Energy analysis of the ML Bragg peaks at the L2 and L3 edges of Co and
Mn reveals the element-specific magnetic moment density profile (MMDP) within the
Co2MnGe layers. We find that the MMDP of Co and Mn are definitely different. In
addition they are more narrow than the chemical density profile and asymmetric with
respect to the growth direction.
We have also studied the interface quality and magnetization profile of [Co2MnGe/V]n
and [Co2MnGe/Al2O3]n multilayers via PNR using the ADAM reflectometers at the
ILL. In the R + map of [Co2MnGe/V]n a half order antiferromagnetic (AF) Bragg peak
occurs at temperatures below 30 K, indicative for weak AF Néel coupling. In contrast,
[Co2MnGe/Al2O3]n multilayers only show FM alignment of the Heusler layers. The
diffuse scattering of the AF peak, as well as the specular intensities of all cross sections
can be described by a domain state in remanence.
[1] J. Schmalhorst et al., Phys. Rev. B 70 (2004) 024426
[2] X. Y. Dong et al., Appl. Phys. Lett. 86 (2005) 102107
[3] J. Grabis et al., Phys. Rev. B 72 (2005) 024438 (2005), J. Grabis et al., Phys.
Rev. B 72 (2005) 024437; A. Bergmann et al., Phys. Rev. B 72 (2005) 214403; A.
Bergmann et al., J. Phys. D: Appl. Phys. 39 (2006) 842
We gratefully acknowledge financial support by the DFG via SFB 491 and BMBF
05KS4PCA and 03ZA6BC1.