Realization of perpendicular magnetic anisotropy and high spin Hall angle in topological semimetal YPtBi/Ta/CoFeB junctions

Abstract YPtBi is a half-Heusler topological semimetal with a large spin Hall angle and high thermal stability. For application to SOT-MRAM, it is essential to fabricate YPtBi/CoFeB junctions with perpendicular magnetic anisotropy (PMA) and high spin Hall angle, which are challenging due to the unfavorable lattice compatibility between YPtBi and CoFeB. In this study, by inserting a Ta spacer layer between YPtBi and CoFeB and optimizing its thickness, we achieved PMA after 300 °C annealing. Subsequently, through optimization of the YPtBi deposition temperature, composition, and CoFeB thickness, we obtained an effective spin Hall angle of θ SH eff = 1.0 and an effective spin Hall conductivity of σ SH eff = 1.6 × 10 5 ( ℏ / 2 e ) Ω − 1 m − 1 for YPtBi. The latter is comparable to or even superior to those obtained using YPtBi/Pt/Co/Pt junctions. Furthermore, we demonstrated SOT-induced magnetization switching with an ultralow current density. These results indicate that YPtBi is a promising candidate for SOT-MRAM.