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

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 (${\sigma }_{SH}\sim 6.5\times 10^5(\hslash /2e){\Omega }^{-1}\cdot m^{-1}$) 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 $J_c\sim 3.2\times 10^{6}A\cdot c{m}^{-2}$ 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.

52 pages, 12 figures, 3 table