Impact of Inherent Energy Barrier on Spin-Orbit Torques in Magnetic-Metal/semimetal Heterojunctions

Spintronic devices are based on heterojunctions of two materials withdifferent magnetic and electronic properties. Although an energy barrier isnaturally formed even at the interface of metallic heterojunctions, its impacton spin transport has been overlooked. Here, using diffusive spin Hallcurrents, we provide evidence that the inherent energy barrier governs the spintransport even in metallic systems. We find a sizable field-like torque, muchlarger than the damping-like counterpart, inNi_81Fe_19/Bi_0.1Sb_0.9 bilayers. This is a distinct signatureof barrier-mediated spin-orbit torques, which is consistent with our theorythat predicts a strong modification of the spin mixing conductance induced bythe energy barrier. Our results suggest that the spin mixing conductance andthe corresponding spin-orbit torques are strongly altered by minimizing thework function difference in the heterostructure. These findings provide a newmechanism to control spin transport and spin torque phenomena by interfacialengineering of metallic heterostructures.