Tunable spin-orbit torque in Cu-Ta binary alloy heterostructures

Abstract

The spin-Hall effect (SHE) is found to be strong in heavy transition metals, such as Ta and W, in their amorphous and/or high resistivity form. In this paper, we show that by employing a Cu-Ta binary alloy as a buffer layer in an amorphous $\mathrm{C}{\mathrm{u}}_{100\ensuremath{-}x}\mathrm{T}{\mathrm{a}}_{x}$-based magnetic heterostructure with perpendicular magnetic anisotropy, the SHE-induced dampinglike spin-orbit torque (DL-SOT) efficiency $|{\ensuremath{\xi}}_{\mathrm{DL}}|$ can be tuned linearly by adjusting the buffer layer resistivity. Current-induced SOT switching can also be achieved in these $\mathrm{C}{\mathrm{u}}_{100\ensuremath{-}x}\mathrm{T}{\mathrm{a}}_{x}$-based magnetic heterostructures, and we find the switching behavior better explained by a SOT-assisted domain-wall propagation picture. Through systematic studies on $\mathrm{C}{\mathrm{u}}_{100\ensuremath{-}x}\mathrm{T}{\mathrm{a}}_{x}$-based samples with various compositions, we determine the lower bound of spin-Hall conductivity $|{\ensuremath{\sigma}}_{\mathrm{SH}}|\ensuremath{\approx}2.02\ifmmode\times\else\texttimes\fi{}{10}^{4}[\ensuremath{\hbar}/2e]{\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}\phantom{\rule{0.28em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}$ in the Ta-rich regime. Based on the idea of resistivity tuning, we further demonstrate that $|{\ensuremath{\xi}}_{\mathrm{DL}}|$ can be enhanced from 0.087 for pure Ta to 0.152 by employing a resistive TaN buffer layer.