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

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 ($ξ_{DL}$) of Pt and Pt alloys have still been limited to $ξ_{DL}$<0.5. Here we present that with proper alloying elements, particularly 3d transition metals V and Cr, a high spin-orbital Hall conductivity ($σ_{SH}{\sim}6.5{\times}10^{5}({\hbar}/2e)Ω^{-1}{\cdot} m^{-1}$) can be developed. Especially for the Cr-doped case, an extremely high $ξ_{DL}{\sim}0.9$ in a Pt$_{0.69}$Cr$_{0.31}$/Co device can be achieved with a moderate Pt$_{0.69}$Cr$_{0.31}$ resistivity of $ρ_{xx}{\sim}133 μΩ{\cdot}cm$. 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 ($α$) 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 $σ_{SH}$, giant $ξ_{DL}$, moderate $ρ_{xx}$, and reduced $α$ of such a Pt-Cr/FM heterostructure makes it promising for versatile extremely low power consumption SOT memory applications.

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