Two-dimensional transition metal dichalcogenides (TMDs) have immense potential for spintronics applications. Here, we report atomic layer thickness dependence in ${\mathrm{WS}}_2/{\mathrm{Co}}_3\mathrm{FeB}$ heterostructures. The layer dependence is predicted by density functional theory and demonstrated experimentally by the layer dependence of the Dzyaloshinskii-Moriya interaction (DMI). Notably, we have observed the DMI in ${\mathrm{WS}}_2$ to be larger than that for heavy metals such as W and Ta, which is important to stabilize chiral structures. Inversion symmetry is not preserved with an odd number of layers, while it exists with an even number of layers. This symmetry rule is reflected in the temperature dependence of the effective damping parameter of the heterostructure. That the damping parameter decreases (increases) in odd (even) layers can be resolved at low temperature. This suggests that the layer dependence has its origin at the ${\mathrm{WS}}_2$ interface, where the spin-valley coupling and spin-orbit coupling activate these features. Large DMI, pure spin current, and unique layer dependence in TMDs provide valuable information and fundamental understanding for designing TMD-based quantum information storage devices.

• Received 23 November 2021
• Revised 19 January 2022
• Accepted 31 January 2022

DOI:https://doi.org/10.1103/PhysRevB.105.064422