Spin current generation in highly conductive Ru/Cu epitaxial heterostructures

Significant spin current generation from highly conductive materials is promising for spintronic applications, such as spin-orbit-torque magnetic random-access memories. In this work, we fabricated epitaxial Ru/Cu heterostructures with interface engineering where 1-nm-thick Ru and Cu layers were alternately deposited at the interface. The spin current generation in the heterostructures was evaluated by unidirectional spin Hall magnetoresistance and spin-torque ferromagnetic resonance. A sizable spin Hall efficiency (~−2%) was achieved in the Ru/Cu sample with a sharp interface which may result from the interface spin filtering effect. Increased spin Hall efficiency (~−4%) was observed in the interface-engineered samples which could be attributed to the intrinsic contribution from lattice distortion and local band structure near the interface. The effective spin Hall conductivity was estimated to be $3\sim 5 \times {10^5}\frac{{h}}{{2e}}{\Omega ^{ - 1}}{{\text{m}}^{ - 1}}$, which is comparable to that of Platinum.