Current-Induced Torques in the Presence of Spin-Orbit Coupling

In systems with strong spin-orbit coupling, the relationship between spin transfer torque and the divergence of the spin current is generalized to a relation between spin transfer torques, total angular momentum current, and mechanical torques. In ferromagnetic semiconductors, where the spin-orbit coupling is large, these considerations modify the behavior of the spin transfer torques. One example is a persistent spin transfer torque in a spin valve: the spin transfer torque does not decay away from the interface but approaches a constant value. A second example is a mechanical torque at a single ferromagnetic-nonmagnetic interface.