Tunable Spin-Orbit Torques in Cu-Ta Binary Alloy Heterostructures

TL;DR

This study demonstrates that the spin Hall effect and spin-orbit torque efficiency in Cu-Ta alloy heterostructures can be linearly tuned by adjusting the buffer layer resistivity, enabling controllable magnetic switching.

Contribution

It introduces a method to tune spin-orbit torque efficiency in magnetic heterostructures using resistivity adjustments in Cu-Ta alloys, with experimental validation.

Findings

SHE-induced damping-like SOT efficiency is tunable via buffer resistivity.

Current-induced SOT switching is achieved and explained by domain wall propagation.

Enhanced SOT efficiency from 0.087 to 0.152 using resistive TaN buffer layer.

Abstract

The spin Hall effect (SHE) is found to be strong in heavy transition metals (HM), such as Ta and W, in their amorphous and/or high resistivity form. In this work, we show that by employing a Cu-Ta binary alloy as buffer layer in an amorphous Cu$_{100-x}$Ta$_{x}$-based magnetic heterostructure with perpendicular magnetic anisotropy (PMA), the SHE-induced damping-like spin-orbit torque (DL-SOT) efficiency $|\xi_{DL}|$ can be linearly tuned by adjusting the buffer layer resistivity. Current-induced SOT switching can also be achieved in these Cu$_{100-x}$Ta$_{x}$-based magnetic heterostructures, and we find the switching behavior better explained by a SOT-assisted domain wall propagation picture. Through systematic studies on Cu$_{100-x}$Ta$_{x}$-based samples with various compositions, we determine the lower bound of spin Hall conductivity $|\sigma_{SH}|\approx2.02\times10^{4}[\hbar/2e]\Omega^{-1}\cdot\operatorname{m}^{-1}$ in the Ta-rich regime. Based on the idea of resistivity tuning, we further demonstrate that $|\xi_{DL}|$ can be enhanced from 0.087 for pure Ta to 0.152 by employing a resistive TaN buffer layer.