Effects of Elemental Doping and Interface Engineering on Spin-Orbit Torques in CoSi-based Topological Semimetal Thin Films

This study reports on how Ni or Fe doping and interface engineering affect the spin-orbit torques (SOTs) generated from the topological semimetal CoSi. The CoSi films deposited on c-plane sapphire substrates are crystalized in a B20 structure and textured in (210) orientation even after 15% Ni or 26% Fe doping. We characterized the SOTs from the films exerted onto the magnetization of a CoFeB layer by harmonic Hall and spin-torque ferromagnetic resonance measurements. The results show that the spin Hall efficiency ξSH of the CoSi decreases after Ni or Fe doping. According to the electrical conductivity dependence of the spin Hall conductivity, which locates at the regime of intrinsic mechanism of spin Hall effect, the reduction of ξSH may result from the degraded topological electronic structures of CoSi by doping. It is also found that inserting a Cu layer at the Co(Ni, Fe)Si/CoFeB interface enhances the ξSH. The enhancement can be due to the improved interfacial spin transparency between the Co(Ni, Fe)Si and CoFeB layers.