In-situ imaging of room-temperature ferromagnetic domains in monolayer vanadium-doped WS₂

Monolayer WS₂ has recently been demonstrated to host long-range, room-temperature ferromagnetic ordering when substitutionally doped with vanadium atoms. V-doped WS₂ and other 2D dilute magnetic semiconductors formed from doped transition metal dichalcogenides are a promising new class of air-stable intrinsic magnetic materials for spintronics applications, but their local magnetic domain structures have not been explored in detail. Here we image magnetic domains in monolayer V-doped WS₂ at different dopant concentrations using in-situ Lorentz Transmission Electron Microscopy (TEM). At low dopant concentration and zero applied field, we observe scattered few-micron-sized ferromagnetic domains with in-plane magnetization. As the out-of-plane applied field strength is increased, the magnetization rotates out-of-plane, aligning with the applied field at ~25 milli Tesla. The domain contrast disappears after repeated exposure to the electron beam, suggesting that radiation damage to the WS₂ destroys the long-range magnetic ordering. In particular, the n-type doping of electron beam-induced sulfur vacancies is suspected to disrupt the ferromagnetic ordering induced by the p-type vanadium doping.