Enhanced ferromagnetism in WS2 via defect engineering

Ferromagnetism in 2D materials has attracted extensive research interests. Defects are expected to play a pivotal role in the ferromagnetism based on theoretical calculations. However, there are few experimental results reported and mechanism of ferromagnetism associated with defects are not clear. In this paper, we employ WS2 powders as an example to study the relationship between defects and magnetism by annealing the powders under reducing atmosphere. Magnetic measurements indicate that pristine WS2 powders show weak ferromagnetism at room temperature. Compared to pristine WS2 powder, annealed samples show significant enhancement of magnetization, which is strongly dependent on annealing temperature. The enhanced magnetization is attributed to defects induced by annealing, evidenced by X-ray photoelectron spectroscopy and electron paramagnetic resonance spectroscopy.