Berlin 2012 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 51: Spin Excitations/ Spin Torque

MA 51.1: Vortrag

Freitag, 30. März 2012, 09:30–09:45, H 1012

Ab initio investigation of the influence of the magnetic material in magnetic tunnel junctions on the bias dependence of the spin-transfer torque — •Christian Franz, Michael Czerner, and Christian Heiliger — I. Physikalisches Institut, Justus-Liebig-Universität, Gießen, Deutschland

We perform an investigation of the material dependence of the bias dependent spin-transfer torque (STT) in magnetic tunnel junctions using ab initio methods. In particular, we investigate Fe, Co and FeCo alloys.

We calculate the STT using a non-equilibrium Green’s function method based on the Keldysh formalism which was implemented in a KKR method. The FeCo alloy is described both by a stacking of Fe and Co layers (ordered alloy) and by the coherent potential approximation (CPA). In the CPA calculations we incorporate non-equilibrium vertex corrections.

Our results show that for an ordered alloy the material of the ferromagnetic layer closest to the barrier has a strong influence on the bias dependence of the STT. Although the size of the STT is nearly independent of the material the qualitative bias dependence changes substantially. When we use the CPA to describe the FeCo alloy different terminations at the interface are mixed. Consequently, the features of the bias dependence of the different pure materials or ordered alloys are washed out. We compare our results to recently presented experimental ones.