Toward 100% Spin-Orbit Torque Efficiency with High Spin-Orbital Hall Conductivity Pt-Cr Alloys

TL;DR

This paper demonstrates that alloying platinum with chromium significantly enhances spin-orbit torque efficiency and spin Hall conductivity, enabling low-power spintronic devices with high performance.

Contribution

The study introduces Pt-Cr alloys with high spin Hall conductivity and efficiency, surpassing previous limitations in Pt-based materials for spin-orbit torque applications.

Findings

Achieved damping-like SOT efficiency of ~0.9 in PtCr/Co devices.

Developed high spin-orbit Hall conductivity (~6.5×10^5 Ω^{-1}·m^{-1}).

Reduced damping constant to 0.052, enabling low switching currents.

Abstract

5d transition metal Pt is the canonical spin Hall material for efficient generation of spin-orbit torques (SOTs) in Pt/ferromagnetic layer (FM) heterostructures. However, for a long while with tremendous engineering endeavors, the damping-like SOT efficiencies (${\xi}_{DL}$) of Pt and Pt alloys have still been limited to ${\xi}_{DL}$<0.5. Here we present that with proper alloying elements, particularly 3d transition metals V and Cr, a high spin-orbital Hall conductivity (${\sigma}_{SH}{\sim}6.5{\times}10^{5}({\hbar}/2e){\Omega}^{-1}{\cdot} m^{-1}$) can be developed. Especially for the Cr-doped case, an extremely high ${\xi}_{DL}{\sim}0.9$ in a Pt$_{0.69}$Cr$_{0.31}$/Co device can be achieved with a moderate Pt$_{0.69}$Cr$_{0.31}$ resistivity of ${\rho}_{xx}{\sim}133 {\mu}{\Omega}{\cdot}cm$. A low critical SOT-driven switching current density of $J_{c}{\sim}3.2{\times}10^{6} A{\cdot}cm^{-2}$ is also demonstrated. The damping constant (${\alpha}$) of Pt$_{0.69}$Cr$_{0.31}$/FM structure is also found to be reduced to 0.052 from the pure Pt/FM case of 0.078. The overall high ${\sigma}_{SH}$, giant ${\xi}_{DL}$, moderate ${\rho}_{xx}$, and reduced ${\alpha}$ of such a Pt-Cr/FM heterostructure makes it promising for versatile extremely low power consumption SOT memory applications.