Description of current-driven torques in magnetic tunnel junctions

A free electron description of spin-dependent transport in magnetic tunnel junctions with non-collinear magnetizations is presented. We investigate the origin of transverse spin density in tunneling transport and the quantum interferences which give rise to oscillatory torques on the local magnetization. Spin transfer torque is also analyzed and an important bias asymmetry is found as well as a damped oscillatory behavior. Furthermore, we investigate the influence of the s-d exchange coupling on torque, in particular in the case of half-metallic MTJs, in which the spin transfer torque is due to interfacial spin-dependent reflections.