Tuning intrinsic ferromagnetic and anisotropic properties of the Janus VSeS monolayer

Motivated by the intrinsic ferromagnetic properties and high Curie temperature of V-based Janus dichalcogenide monolayers as a new class of 2D materials, we investigated the structural, electronic and magnetic properties of the Janus VSeS monolayer by first-principles calculations. By focusing on the 2H phase, which is energetically more favorable than the 1T phase, we show that the spin orientation has a profound effect on the dynamical stability and electronic structure of the VSeS monolayer. Transition from non-magnetic to magnetic phase opens a band gap and switching from anti-ferromagnetic (AFM) to ferromagnetic (FM) phase eliminates imaginary modes of phonon dispersion and stabilizes the monolayer. Magnetic and anisotropic phase diagrams of the ferromagnetic VSeS monolayer are also studied under an applied biaxial strain. Tensile strain enhances the FM coupling by modifying through-bond and through-space interactions. Magnetic anisotropy energy is tunable by charge doping and a small carrier concentration can induce a transition from a ferromagnetic semiconductor to a half-metal. Moreover, by means of the 2D XY model, we estimate that the Berezinskii-Kosterlitz-Thouless (BKT) transition to a quasi-long-range ordered phase occurs at 83 K. We also simulate a vertical van der Waals heterostructure of VSeS/hBN to study not only the magnetic proximity effect, but also the magnetic properties of the VSeS monolayer on a substrate. The results indicate that the heterostructure is a ferromagnetic semiconductor and the VSeS monolayer preserves its magnetic properties, demonstrating high potential for application in spintronics.