Structural and electronic phase transitions in ferromagnetic monolayer VS2 induced by charge doping

Among the known transition metal dichalcogenides, monolayer ${\mathrm{VS}}_{2}$ has attracted particular attention because of its intrinsic ferromagnetism and great application potential as a high-performance functional nanomaterial. Here, using first-principles calculations, we study the structural and electronic phase transitions in monolayer ${\mathrm{VS}}_{2}$ induced by charge doping. We show that without electron or hole doping, ${\mathrm{VS}}_{2}$ stabilizes in the 2H phase and is a bipolar magnetic semiconductor (BMS) whose valence and conduction states near the Fermi level carry opposite spin polarization. With the increase of hole doping concentration, ${\mathrm{VS}}_{2}$ will first experience an electronic phase transition from a BMS to a half metal, followed by a 2H-to-1T structural phase transition (SPT) which concomitantly results in another electronic phase transition from the half metal to a normal metal. Moreover, the reduced reaction barrier from the 2H to 1T phases by hole doping can make the occurrence of the SPT easier. However, electron doping can only induce the BMS-to-half metal electronic phase transition but will not trigger the SPT within the experimentally accessible doping regime. The different effects of hole and electron dopings on the SPT are further explained by the energy band diagram of ${\mathrm{VS}}_{2}$. These results establish the potential for ${\mathrm{VS}}_{2}$ utilization in innovative phase-change electronic and spintronic devices.