Dimension-dependent phase transition and magnetic properties of VS ₂

Among dozens of layered transition metal dichalcogenides (TMDs), VS ₂ has attracted particular interest due to its intrinsic magnetism and potential applications as a high-performance functional nanomaterial. The phase stability and electronic properties of the typical crystal structures of both monolayer and bulk VS₂ are carefully investigated based on first-principle calculations. The results reveal that the relative stability between different phases is greatly affected by the thickness of the layers and the temperature. Below room temperature, both bulk and monolayer VS₂ prefer to exhibit the hexagonal (H) structure instead of the trigonal (T) structure. Interestingly, at room temperature, although the H monolayer VS ₂ remains more stable than the T-VS₂, the bulk T-VS ₂ becomes more stable than H-VS₂. These results reveal that a phase transition between H and T will occur on changing either the thickness of the slab or the temperature. Furthermore, the different crystal structures (H and T) exhibit significantly distinct magnetism: the bulk T-VS₂ has the lowest magnetism (0.31 μ_B), while the monolayer H-VS₂ has the largest magnetism (about 1.00 μ_B) among the structures. Most importantly, our results reveal that the magnetism will increase sharply on the exfoliation of monolayer VS ₂ from the bulk at room temperature because of the phase transition from T to H. The present results provide an efficient way to modulate the magnetic moment through controlling the crystal structure and the thickness of the VS₂ nanosheets.