Current induced torques and interfacial spin-orbit coupling: semiclassical modeling
Paul M. Haney, Hyun-Woo Lee, Kyung Jin Lee, Aurelien Manchon, Mark D. Stiles
Currents passing through bilayer nanowires with a ferromagnetic layer and a non-magnetic layer with strong spin-orbit coupling, excite magnetic dynamics which cannot be explained with standard models. The dynamics appear to require two torques which can be characterized as damping-like and field-like. Typically very different models yield the different torques. A model based on the Boltzmann nist-equation can unify these approaches. It combines both torques due to the bulk spin Hall effect and the spin transfer torque and torques due to the interfacial spin-orbit coupling. An approximation to the Boltzmann nist-equation, the drift-diffusion model, qualitative reproduces the behavior, but quantitatively fails to reproduce the results. While the Boltzmann nist-equation with appropriate parameters can match the torques for any particular sample, it fails to describe the experimentally observed thickness dependences in many cases. This disagreement suggests that the parameters describing the system vary as the thicknesses do.