Maximizing spin–orbit torque efficiency of Ta(O)/Py via modulating oxygen-induced interface orbital hybridization

Abstract

Spin–orbit torques due to interfacial Rashba and spin Hall effects have been widely considered as a potentially more efficient approach than the conventional spin-transfer torque to control the magnetization of ferromagnets. We report a comprehensive study of spin–orbit torque efficiency in Ta(O)/Ni81Fe19 bilayers by tuning low-oxidation of β-phase tantalum and find that the spin Hall angle θDL increases from ∼−0.18 of the pure Ta/Py to the maximum value ∼−0.30 of Ta(O)/Py at 7.8% oxidation. Furthermore, we distinguish the spin–orbit torque efficiency generated by the bulk spin Hall effect and interfacial Rashba effect, respectively, via a series of Ta(O)/Cu(0–2 nm)/Py control experiments. The latter has more than twofold enhancement and is even more significant than the former at the optimum oxidation level. Our results indicate that 65% enhancement of the efficiency should be related to the modulation of the interfacial Rashba-like spin–orbit torque due to oxygen-induced orbital hybridization across the interface. Our results suggest that the modulation of interfacial coupling via oxygen-induced orbital hybridization can be an alternative method to boost the change-spin conversion efficiency.