Enhancement of spin-orbit torque in WS2/Co/Pt trilayers via spin-orbit proximity effect

Enhancement of spin-orbit torque (SOT) efficiency in ferromagnet/heavy-metal bilayer is promising for the realization of low-power spintronic devices. Here we show that inserting a single-layer WS2 between the substrate and Co/Pt layers, can reduce Co coercivity by similar to 28% and increase dampinglike SOT efficiency by similar to 30%, up to 35.07 Oe/(107A/cm2). When inserting WS2 with different layers, we further demonstrate that these phenomena only exist for odd WS2 layers, i.e., monolayer and trilayer, while they disappear for even WS2 layers, i.e., bilayer. Theoretical analysis based on the first-principles calculations suggests that the results originate from the thickness-controlled charge transfer between WS2 and Co, which is consistent with the spin-orbit proximity effect.