Influence of spin-orbit coupling on the transport properties of magnetic tunnel junctions

Using a fully relativistic implementation of the Landauer-Buttiker formalism, the ballistic conductance and magnetoresistance in the Fe/GaAs/Fe tunnel junction has been calculated. The underlying electronic structure of the system was obtained using a spin-polarized relativistic version of the screened Korringa-Kohn-Rostoker Green-function method. To analyze the influence of spin-orbit coupling induced spin-flip processes on the spin-dependent transport, a scheme introduced recently by us which allows one to split the relativistic conductance in terms of individual spin-diagonal and spin off-diagonal (spin-flip) components has been applied. Our previous investigations showed that a strong spin-flip channel is present in the conductance, having the most important influence for an antiparallel alignment of the magnetization in the two Fe leads. Motivated by these findings and based on model calculations in which the strength of the spin-orbit interaction has been manipulated we present a detailed analysis of the various features induced by the spin-orbit coupling inside the barrier, and how these modify the tunneling. We found that even in the ideal case of a specular interface the magnetoresistance can significantly drop if the spacer is characterized by a strong spin-orbit coupling.