It is of great significance in the memory industry to find a conductive spin current source (SCS) possessing a large damping-like spin-orbit torque efficiency (ξDL) higher than W, for the purpose of realizing a faster and more efficient spin-orbit torque magnetic random-access memory (SOT-MRAM). Among numerous candidates, 5d transition metal Pt is one of the more competitive spin Hall materials for efficiently generating spin-orbit torques (SOTs) in Pt/ferromagnetic layer (FM) heterostructures, due to its high spin Hall conductivity (SHC) and moderate resistivity. However, for a long while with tremendous engineering endeavors, the of Pt and Pt alloys are still limited to ξDL<0.5 . In this work, we report that with proper alloying elements, particularly the 3d transition metals V and Cr with giant orbital Hall effect (OHE), the strength of the high spin Hall conductivity of Pt (σSH~6.45×105 (h-bar/2e) Ω-1 m-1) is observed even in the relatively resistive regime. Especially for the Cr-doped case, an extremely high ξDL~0.9 in a perpendicular magnetized Pt0.69Cr0.31/Co device can be achieved with a moderate Pt0.69Cr0.31 resistivity of ρxx~133 μΩ cm . This sizable SOT efficiency can be attributed to the additional spin current generation from orbital-to-spin current conversion, resulting in the increasing SHC as the Cr concentration in the Pt-Cr alloy increases. Moreover, a low critical SOT-driven switching current density of is also demonstrated, and the damping constant (α) of Pt0.69Cr0.31/CoFeB structure is found to be reduced to 0.052 from the pure Pt/CoFeB case of 0.078. The overall high σSH, giant ξDL, moderate ρxx , and the reduction of α make the Pt-Cr/FM heterostructure promising for versatile extremely low power consumption SOT memory applications.
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Damping-like spin-orbit torque efficiency of PtxCr1-x alloys in Pt-Cr/Co structures.