Enhancement of the spin–orbit torque efficiency in W/Cu/CoFeB heterostructures via interface engineering

Abstract

Here, the spin-torque ferromagnetic resonance signal and the spin Hall magnetoresistance induced by the spin Hall effect of W/Cu/CoFeB heterostructures with different Cu layer thicknesses (tCu) have been systemically studied. The effective spin mixing conductance geff↑↓, the interfacial spin transparency T, and the real spin–orbit torque efficiency (JsJc)real show a significant increase compared to the W/CoFeB heterostructure. (JsJc)real reaches its maximum of ∼0.54, increased up to ∼50% at the optimized tCu ∼ 0.52 nm according to our theoretical prediction. More importantly, the intrinsic spin Hall angle of W, θSHint ∼ 0.79 ± 0.20, has also been obtained after the correction of the inverse spin Hall effect and T. This suggests that the Cu insertion improves the interface quality and, therefore, assists the spin transport in the heterostructures, which potentially improves the performance of next-generation spintronic devices.