Orbital torque in Mn/FM bilayer systems

Abstract

We investigate the orbital torque generated in ferromagnetic (FM)/manganese (Mn) bilayer systems based on angular-dependent spin-torque ferromagnetic resonance (ST-FMR) experiments. From the ST-FMR results, it is found that a relatively large out-of-plane anti-damping torque can be obtained in Ni/Mn bilayers. The Gilbert damping constant, derived from the resonant linewidth of frequency-dependent ST-FMR experiments, decreases almost linearly with increasing thickness of Mn, further indicating the out-of-plane anti-damping torque in Ni/Mn bilayer systems. The origin of this torque can be attributed to the orbital Rashba–Edelstein effect. Furthermore, the orbital diffusion length (λL) in Mn is determined to be more than 17 nm and larger than spin diffusion length, suggesting that the torque observed in our sample is predominantly influenced by the orbital-related effect. Finally, the insertion of Pt in a Ni/Mn bilayer system significantly enhances the orbital-to-spin conversion efficiency. These results clearly demonstrate that Mn is a promising material for future orbitronics devices.