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

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 (t(Cu)) have been systemically studied. The effective spin mixing conductance g(eff)(up arrow down arrow), the interfacial spin transparency T, and the real spin-orbit torque efficiency (J(s)/J(c))(real) show a significant increase compared to the W/CoFeB heterostructure. (J(s)/J(c))(real) reaches its maximum of similar to 0.54, increased up to similar to 50% at the optimized t(Cu) similar to 0.52nm according to our theoretical prediction. More importantly, the intrinsic spin Hall angle of W, theta(hint)(SH) similar to 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.