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 (τ ∥) and out-of-plane torque (τ ⊥) 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.