Regensburg 2007 – scientific programme
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MA: Fachverband Magnetismus
MA 8: Magnetic Materials II
MA 8.1: Talk
Monday, March 26, 2007, 15:15–15:30, H22
New half-metallic ground state in non-ideal Co2−xMn1+xSi — •Björn Hülsen1, Peter Kratzer2, and Matthias Scheffler1 — 1Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin — 2Fachbereich Pysik, Universität Duisburg-Essen, Lotharstr. 1, D-47048 Duisburg
The half-metallic full Heusler alloy Co2MnSi is a promising candidate for spintronics applications. Heterostructures like magnetic tunnel junctions where Co2MnSi is incorporated with metal oxide layers are annealed with temperatures of 400 − 500∘C during the growth process. To access the finite-temperature properties of Co2MnSi we apply a combined approach of density functional theory (DFT), cluster expansion (CE), and Monte Carlo (MC) techniques. Since the most abundant defects in Co2MnSi are Mn and Co antisites which are also the ones that influence the electronic structure most significantly, we regard Co2MnSi as a pseudo-binary alloy and perform a CE that takes only the interactions between the Co and Mn atoms into account, while the Si atoms are confined to their sublattice. The coefficients of this CE are fitted to the energies of 59 structures that have been determined by DFT calculations using the full-potential linearized augmented plane wave method. Two of the seven predicted ground states show a spin gap, one is the well known L21 structure while the new half-metallic ground state has a Mn concentration of 50%. The effective Hamiltonian is used as input for a simulated annealing of ideal and non-ideal compositions of Co2−xMn1+xSi that allow the computation of the equilibrium configurations of these structures.