Berlin 2012 – scientific programme

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MA: Fachverband Magnetismus

MA 35: Magnetic Heusler Compounds I

MA 35.8: Talk

Wednesday, March 28, 2012, 17:15–17:30, H 0112

Electronic properties of Co₂Fe_xMn_1−xSi Heusler alloys studied by hard X-ray photoelectron spectroscopy. — •A. Gloskovskii¹, S. Thiess³, S. Ouardi¹, G. H. Fecher^{1, 2}, W. Drube³, B. Detlefs⁴, T. Kubota⁵, Y. Ando⁵, and C. Felser^{1, 2} — ¹Institute of Inorganic Chemistry and Analytical Chemistry, JoGu University, Mainz — ²Max Planck Institute for Chemical Physics of Solids, Dresden — ³Deutsches Elektronen-Synchrotron DESY, Hamburg — ⁴ESRF, Grenoble — ⁵Department of Applied Physics, Graduate School of Engineering, Tohoku University, Sendai

Fully epitaxial magnetic tunnel junctions (MTJs) with a Co₂YZ thin film as a base electrode and a MgO tunnel barrier exhibit high TMR ratios. Quaternary Co₂Fe_xMn_1−xSi (CFMS) Heusler alloys are even more promising because the substitution of Mn by Fe increases the number of valence electrons and therefore leads to higher Curie temperatures above 1000 K. The maximum TMR ratio for CFMS-CoFe MTJs was found for Fe fractions of between x=0.4 and 0.6. Half-metallicity disappears for the samples with x≥0.8.

A B2 and L2₁ site ordered stack of MgO substrate/ Cr [40 nm] buffer layer/Co₂Fe_xMn_1−xSi [30 nm]/MgO[2 nm]/AlO_x [1.3 nm] (x = 0, 0.2 … 1.0) films was studied at beamline P09 at PETRA III and beamline ID32 at the ESRF. The hard X-Ray photoelectron spectroscopy (HAXPES) studies were performed with an excitation energy of 6 keV. It was found that the position of Co 2p core levels and the density of states in the valence band region strongly depend on the Fe/Mn ratio.