Reduction of spin backflow with underlying bulk WSe2 in Pt/Py/Al trilayers

To enhance spin–orbit torque (SOT) efficiency, various approaches exist, including the modification of spin mixing conductance through interface engineering. Recent studies have highlighted that transition metal dichalcogenides with strong spin–orbit couplings serve as spin sources and sinks even in few-layer configurations. In this study, we carry out spin torque ferromagnetic resonance measurements on SOT devices with insertion of a bulk WSe2 underlayer and reveal a notable increase in their spin mixing conductance and damping-like torque efficiency. Using the spin transparency model, we quantitatively unveil the reduction of the spin backflow factor, verifying the role of spin sink layers in SOT modification.