Nonlocal Spin-Orbit Torques

Spin-orbit torque is a current-induced transfer of angular momentum from an atomic lattice to magnetic order. It is a promising mechanism to write magnetic memories and drive spin torque oscillators. Since its inception, the list of spin-orbit torque mechanisms has grown beyond the conventional spin Hall and Rashba-Edelstein mechanisms to include “unconventional” mechanisms, arising from spin and orbital current generation in ferromagnetic layers, nonmagnetic layers, and their interfaces. However, the role of interlayer scattering—which is responsible for the current-in-plane giant magnetoresistance—is not typically considered when analyzing spin-orbit torque. In this talk, we use symmetry analysis, semiclassical models, and first principles calculations to show that nonlocal spin-orbit torques driven by interlayer scattering are potentially important for devices. First, we theoretically demonstrate the existence of nonlocal spin torques in ferromagnetic trilayers through ab-initio calculations, which show that such torques are as large as conventional dampinglike torques from the spin Hall effect in Pt. We then use semiclassical calculations to qualitatively reproduce these results and suggest an extrinsic mechanism due to interlayer spin-orbit scattering. Understanding the role of nonlocal torques in ferromagnetic trilayers should help to accurately interpret experiments and optimize spin-orbit torque for future spintronic applications.