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

This work reports on Ni and Fe doping and interface effects on spin-orbit torques (SOTs) generated from a topological semimetal CoSi. CoSi thin films grown on Al2O3(0001) substrates by magnetron co-sputtering show the B20 structure with a texture in the [210] orientation even after Ni or Fe doping. The SOTs from the films exerted on the magnetization of a CoFeB layer are evaluated by harmonic Hall and spin-torque ferromagnetic resonance measurements. The spin Hall efficiency xi(SH) of the textured B20-CoSi at room temperature is determined to be 9.6%, which decreases to 1.8% for Ni0.15Co0.85Si and to 5.5% for Fe0.26Co0.74Si. The electrical conductivity dependence of the spin Hall conductivity is assigned to the regime of intrinsic mechanism of spin Hall effect, suggesting that the reduction of xi(SH) with the element doping can be due to the degradation in topological electronic structures of CoSi. Furthermore, inserting a Cu layer at the Co(Ni, Fe)Si/CoFeB interface results in an increase of the xi(SH) up to 10.9% for CoSi, 4.0% for Ni0.15Co0.85Si, and 8.3% for Fe0.26Co0.74Si. These enhancements of the xi(SH) can be attributed to the improvement in the interfacial spin transparency between the Co(Ni, Fe)Si and CoFeB layers.

Automated summary

This work investigates the effects of Ni and Fe doping and interface properties on spin-orbit torques (SOTs) in a topological semimetal CoSi. It is found that the doping of Ni and Fe reduces the spin Hall efficiency, while the insertion of a Cu layer at the interface enhances the spin Hall efficiency.