Interfacial Spin-Orbit Torques and Magnetic Anisotropy in WSe₂/Permalloy Bilayers

In recent years, there has been a growing interest in spin-orbit torques (SOTs) for magnetization manipulation in non-volatile magnetic memory devices. SOTs rely on the spin-orbit coupling of a nonmagnetic material, such as transition metal dichalcogenides (TMDs), coupled to a ferromagnet (FM) to convert a charge current into a torque on the FM’s magnetization. However, there is still no consensus on the microscopic origin of SOTs in TMD/FM bilayers.

To address this issue, we perform thickness-dependent SOT measurements in WSe₂/permalloy heterostructures, down to the monolayer limit. We observe large out-of-plane field-like torques, and for some devices, smaller in-plane antidamping-like torques, both with no clear thickness dependence. Our results strongly point to a Rashba spin-orbit coupling at the TMD/FM interface as the key ingredient for SOTs in these systems. Unexpectedly, we also observe a strong in-plane magnetic anisotropy induced in permalloy along the armchair crystal direction of the WSe₂ flake. Our results unveil the nature of the SOTs in TMD-based devices and their interaction with FM layers, highlighting the potential of TMDs for non-volatile devices for data processing and storage.