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 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.

Phase Transition and Oxidation Dependence of Charge–Spin Conversion in Rare‐Earth Gadolinium

“…According to a previous report, [ 31,32 ] there was a significant ξ enhancement that originated from the oxidation of the metal. To quantitatively determine the effect of ambient oxidation in the Gd layer on ξ , we acquired ST‐FMR frequency spectra at 300 K. Figure a,b shows the ST‐FMR resonance signal V dc for MgO/Py/GdO x (10 nm) and MgO/Py/GdO x (20 nm) at φ = 45°.…”

“…However, because of the 30‐day air exposure, the 10 nm GdO x sample had a Gd/GdO x interface in the Gd layer. Thus, the Rashba–Edelstein effect at the Gd/GdO x interface also allowed significant charge–spin conversion and generated comparable spin currents, [ 32 ] except for the bulk SHE in Gd. Because the level of oxidation was weaker in the 20 nm GdO x sample (according to the ratio of the oxidation layer to the total Gd thickness), bulk SHE in Gd dominated the charge–spin conversion rather than the interfacial Rashba–Edelstein effect.…”

Enhancement of spin-orbit torque efficiency by tailoring interfacial spin-orbit coupling in Pt-based magnetic multilayers

“…Figure 1(b) shows the representative ST-FMR spectra of Pt(5)/Co(0.4)/Py(4) sample with excitation frequency from 6 to 10 GHz, IP angle 𝜑 = 30°. The obtained 𝑉 mix can be well fitted with a Lorentzian function [1,23]:…”

“…The effective demagnetization field 4π𝑀 eff = 4π𝑀 s − 𝐾 eff 2π𝑀 s ⁄ for all studied ST-FMR devices can be obtained by fitting the experimental results of f vs. Hres [Fig. 2 (a)] using the Kittel formula [23]: 𝑓 = (𝛾 2π ⁄ )√𝐻 res (𝐻 res + 4π𝑀 eff ), where 𝛾 2π ⁄ is the gyromagnetic ratio. From the intercept of the linear fitting with Eq.…”

“…To further examine how the above Pt/Co interfacial characteristics of Ks, 𝐺 eff,tot ↑↓ and the coefficient 𝛽 TMS are reflected in the 𝜉 DL and 𝜉 FL , we adopt two methods of lineshape analysis (𝑉 s 𝑉 a ⁄ ) and linewidth modulation (LWM) to quantify the SOTs via the ST-FMR spectra. Based on the previous reports[1,23] of the HM/FM bilayer system with the conventional SHE/IREE, the 𝑉 𝑠 and 𝑉 𝑎 components originate from the OP DL effective field HDL and IP Oersted field HOe and/or FL effective field HFL, respectively. Therefore, the spin-torque efficiency (𝜉 FMR ) can be estimated by the tot ⁄ and 𝐻 Oe is independent of 𝑡 FM tot .…”