The effects of substitutional Fe-doping on magnetism in MoS2 and WS2 monolayers

Doping of two-dimensional (2D) semiconductors has been intensively studied toward modulating their electrical, optical, and magnetic properties. While ferromagnetic 2D semiconductors hold promise for future spintronics and valleytronics, the origin of ferromagnetism in 2D materials remains unclear. Here, we show that substitutional Fe-doping of MoS2 and WS2 monolayers induce different magnetic properties. The Fe-doped monolayers are directly synthesized via chemical vapor deposition. In both cases, Fe substitutional doping is successfully achieved, as confirmed using scanning transmission electron microscopy. While both Fe:MoS2 and Fe:WS2 show PL quenching and n-type doping, Fe dopants in WS2 monolayers are found to assume deep-level trap states, in contrast to the case of Fe:MoS2, where the states are found to be shallow. Using μm- and mm-precision local NV− magnetometry and superconducting quantum interference device, we discover that, unlike MoS2 monolayers, WS2 monolayers do not show a magnetic phase transition to ferromagnetism upon Fe-doping. The absence of ferromagnetism in Fe:WS2 is corroborated using density functional theory calculations.