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 (ζDL) of Pt and Pt alloys have still been limited to ζDL< 0.5. Here we present that with proper alloying elements, particularly 3d transition metals V and Cr, a high spin-orbital Hall conductivity (σSH≈ 6.5 × 105(/2e) ω-1m-1) can be developed. Especially for the Cr-doped case, an extremely high ζDL≈ 0.9 in a Pt0.69Cr0.31/Co device can be achieved with a moderate Pt0.69Cr0.31resistivity of ρxx≈ 133 μω cm. A low critical SOT-driven switching current density of Jc≈ 3.2 × 106A cm-2is also demonstrated. The damping constant (α) of the Pt0.69Cr0.31/FM structure is also found to be reduced to 0.052 from the pure Pt/FM case of 0.078. The overall high σSH, giant ζDL, moderate ρxx, and reduced α of such a Pt-Cr/FM heterostructure makes it promising for versatile extremely low power consumption SOT memory applications.