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 βphase 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 with 7.8% oxidation. Furthermore, we distinguish the efficiency of the spin-orbit torque generated by the bulk spin Hall effect and by interfacial Rashba effect, respectively, via a series of Py/Cu(0-2 nm)/Ta(O) control experiments. The latter has more than twofold enhancement, and even more significant than that of 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 cross the interface. Our results suggest that the modulation of interfacial coupling via oxygen-induced orbital hybridization can be an alternative method to boost the changespin conversion rate.

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We investigate properties of perpendicular anisotropy magnetic tunnel junctions (pMTJs) with a stack structure MgO/CoFeB/Ta/CoFeB/MgO as the free layer (or recording layer), and obtain the necessary device parameters from the tunneling magnetoresistance (TMR) vs. field loops and current-driven magnetization switching experiments. Based on the experimental results and device parameters, we further estimate current-driven switching performance of pMTJ including switching time and power, and their dependence on perpendicular magnetic anisotropy and damping constant of the free layer by SPICE-based circuit simulations. Our results show that the pMTJ cells exhibit a less than 1 ns switching time and write energies < 1.4 pJ; meanwhile the lower perpendicular magnetic anisotropy (PMA) and damping constant can further reduce the switching time at the studied range of damping constant α < 0.1. Additionally, our results demonstrate that the pMTJs with the thermal stability factor ≃ 73 can be easily transformed into spin-torque nano-oscillators from magnetic memory as microwave sources or detectors for telecommunication devices.