Spin-Torque Generation from Cu Oxides

Current-induced spin-orbit torques provide an effective way to manipulate the magnetization in spintronic devices, which promises ultralow energy consumption memory and logic devices. However, it has been believed that heavy metals are indispensable for generating the spin-orbit torques. Here, we report that Cu, which is an earth abundant light metal, generates sizable spin-orbit torques, triggered by precise tuning of the oxidation level. In this work, we investigate the generation efficiency of the spin-orbit torques from homogeneously oxidized Cu using the spin-torque ferromagnetic resonance (ST-FMR) technique for Ni₈₁Fe₁₉/CuO_x bilayers. We demonstrate that the damping-like torque generated from CuO_x is dramatically enhanced by the controlled oxidation only within a narrow range of the oxidation level, which is concomitant with the sign reversal of the field-like torque. We also show that the spin-orbit torques are generated from a highly oxidized Cu where a bulk charge current is negligible, indicating that interface spin-orbit coupling is responsible for the efficient spin-torque generation in this system.