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 (ξDL) of Pt and Pt alloys have still been limited to ξDL < 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 (ℏ/2e) Ω–1 m–1) can be developed. Especially for the Cr-doped case, an extremely high ξDL ≈ 0.9 in a Pt0.69Cr0.31/Co device can be achieved with a moderate Pt0.69Cr0.31 resistivity of ρxx ≈ 133 μΩ cm. A low critical SOT-driven switching current density of Jc ≈ 3.2 × 106 A cm–2 is 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 ξDL, moderate ρxx, and reduced α of such a Pt–Cr/FM heterostructure makes it promising for versatile extremely low power consumption SOT memory applications.