Regensburg 2013 – scientific programme

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MA: Fachverband Magnetismus

MA 8: Spin Excitations and Spin Torque

MA 8.7: Talk

Monday, March 11, 2013, 11:15–11:30, H23

Concentration dependence of the tunnel magnetoresistance and spin-transfer torque in FeCo/MgO/FeCo 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 magnetic 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. We describe the transport processes using a non-equilibrium Green’s function method, which was implemented in a KKR method. The FeCo alloys are described by the coherent potential approximation (CPA). In the CPA calculations we incorporate non-equilibrium vertex corrections. The alloy scattering, which is included in the CPA description, leads to a broadening of the bands. As a result, we find that in the voltage dependence of TMR and STT resonant features are smeared out for finite concentrations. For zero bias the TMR shows only a weak concentration dependence for intermediate concentrations but a strong enhancement towards the pure components. At a finite bias of 0.54 V we find that the TMR strongly decreases with the Co concentration. The investigation of the concentration dependence of the STT shows that, while the interlayer exchange coupling decreases with the Co concentration, the linear bias dependence of the in-plane-torque is independent of the concentration. Thus our results favour high Fe concentrations in order to obtain a high TMR and STT.