Dresden 2014 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 55: Poster II

MA 55.4: Poster

Freitag, 4. April 2014, 10:30–13:30, P2

Material and bias dependence of the tunnel magnetoresistance and spin-transfer torque in magnetic tunnel junctions — •Christian Franz, Michael Czerner, and Christian Heiliger — I. Physikalisches Institut, Justus Liebig University, Giessen, Germany

We investigate magnetic tunnel junctions with Fe_1−xCo_x alloys as ferromagnetic layers and a MgO barrier. We calculate ab initio the tunnel magnetoresistance (TMR) and spin-transfer torque (STT) for zero and finite bias voltage and analyze their dependence on the concentrations [1]. The transport properties are obtained using a non-equilibrium Green’s function method. The FeCo alloys are described by the coherent potential approximation (CPA) including vertex corrections [2].

The disorder scattering, which is included by the CPA description, leads to diffusive currents. These lead to a drop in the TMR at zero bias from large values for the pure materials to around 2000% at finite concentrations. At a large bias we find that the TMR decreases with the Co concentration as a result of the band filling. Likewise, the TMR decreases much faster with increasing bias voltage for pure Co leads than for smaller Co concentrations. The in-plane and out-of-plane STT show linear and quadratic voltage dependence at small bias for all concentrations. The linear slope of the in-plane STT is independent of the concentration. At large bias voltages, we find strong deviations from this dependence for high Co concentrations.

[1] C. Franz et. al, Phys. Rev. B 88, 094421 (2013)

[2] C. Franz et. al, J. Phys.: Condens. Matter 25, 425301 (2013)