Self-consistent treatment of nonequilibrium spin torques in magnetic multilayers

It is known that the transfer of spin angular momenta between current carriers and local moments occurs near the interface of magnetic layers when their moments are noncollinear. However, to determine the magnitude of the transfer, one should calculate the spin transport properties far beyond the interface regions. Based on the spin-diffusion equation, we present a self-consistent approach to evaluate the spin torque for a number of layered structures. One of the salient features is that the longitudinal and transverse components of spin accumulations are intertwined from one layer to the next, due to the presence of the much longer longitudinal spin-diffusion length and thus, the spin torque could be significantly amplified with respect to treatments which concentrate solely on the transport at the interface. We conclude that bare spin currents do not properly estimate the spin angular momentum transferred between the magnetic background; the spin transfer that occurs at interfaces should be self-consistently determined by embedding it in our globally diffuse transport calculations.