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 ${\mathrm{WS}}_2$ between the substrate and Co/Pt layers, can reduce Co coercivity by $\sim 28\%$ and increase dampinglike SOT efficiency by $\sim 30\%$, up to 35.07 Oe/$\left({10}^7\mathrm{A}\text{/}{\mathrm{cm}}^2\right)$. When inserting ${\mathrm{WS}}_2$ with different layers, we further demonstrate that these phenomena only exist for odd ${\mathrm{WS}}_2$ layers, i.e., monolayer and trilayer, while they disappear for even ${\mathrm{WS}}_2$ layers, i.e., bilayer. Theoretical analysis based on the first-principles calculations suggests that the results originate from the thickness-controlled charge transfer between ${\mathrm{WS}}_2$ and Co, which is consistent with the spin-orbit proximity effect.

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• First-principles calculations
• Spin-orbit torque
• Transition metal dichalcogenides
• Hall bar
• Sputtering