Spin-orbit torques in GaN/NiFe bilayers

We report the study of spin-orbit torques in different GaN/NiFe bilayers using a spin-torque ferromagnetic resonance (ST-FMR) method. The GaN/NiFe bilayer based on Ge-GaN and Fe-GaN displayed distinct ST-FMR results, i.e. voltage signal intensity, lineshape, and resonance field. The Ge-GaN/NiFe bilayer exhibited a stronger torque ratio between in-plane torque (tau(parallel to)) and out-of-plane torque (tau(perpendicular to)) than the Fe-GaN/NiFe bilayer, which can be ascribed to the difference of Fermi energy level in Ge-GaN and Fe-GaN. Furthermore, the torque ratio of both systems tends to decrease with microwave frequency. Our results may help to understand the spin-orbit torques in GaN.