Current-induced torque dominated by the orbital Hall effect in Au

Abstract

We report current-induced torque generated by the orbital Hall effect in Au. Although Au is a heavy metal with strong spin–orbit coupling, its spin Hall effect is intrinsically weak, making it a suitable platform for investigating orbital Hall physics in a regime analogous to light metals, where spin Hall contributions are negligible. Using spin-torque ferromagnetic resonance, we quantify the damping-like torque efficiency in Au/ferromagnet bilayers. We find that the Au/Ni bilayers exhibit a sizable damping-like torque comparable to that of Pt-based systems, whereas the damping-like torque in Au/Ni81Fe19 bilayers remains negligible over the same Au thickness range, highlighting the minor role of the spin Hall effect. Furthermore, the damping-like torque efficiency in the Au/Ni bilayers increases with increasing Au thickness, consistent with a bulk contribution from the orbital Hall effect in Au. These results show that orbital currents play a dominant role in current-induced torques in this system and provide experimental insight into orbital-dominated torque generation in heavy-metal systems.