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.