Giant Enhancement of Spin‐Orbit Torque Efficiency in Pt/Co Bilayers by Inserting a WSe2 under Layer

Abstract 2D transition metal dichalcogenides (TMDs) are excellent candidate materials to study the effect of spin‐orbit torques (SOTs). Here, the effect of a WSe 2 underlayer on the magnetic properties and SOT efficiencies are systematically investigated in Pt /Co bilayers with perpendicular magnetic anisotropy. SOT efficiency ξ shows an increasing trend as the inserted WSe 2 monolayer number increases from 0 to 5, which is attributed to the elevated spin absorption at the WSe 2 /Pt interface where WSe 2 acts as a spin sink. As the Co layer thickness t Co increases from 0.6 to 1.0 nm, ξ exhibits a maximum at t Co = 0.8 nm, which is mainly due to the nonmonotonic change of spin transmission at the Pt/Co interface. Moreover, the ξ value of WSe 2 (5ML) /Pt/Co increases significantly when the measurement temperature decreases, which can be interpreted by the increased spin absorption capability of WSe 2 due to the elevated spin mixing conductance at reduced temperatures. The findings provide deep insight into the origin of robust charge‐spin conversion in the TMD/Pt/Co system, which will promote the implementation of advanced SOT devices based on the 2D materials.