Two-dimensional XY ferromagnetism above room temperature in Janus monolayer V2XN (X = P, As).

Two-dimensional (2D) XY magnets with easy magnetization planes support the nontrivial topological spin textures whose dissipationless transport is highly desirable for 2D spintronic devices. Here, we predicted that Janus monolayer V2XN (X = P, As) with a square lattice is a 2D-XY ferromagnet using first-principles calculations. Both magnetocrystalline anisotropy and magnetic shape anisotropy favor an in-plane magnetization, leading to an easy magnetization xy-plane in Janus monolayer V2XN. With the help of the Monte Carlo simulations, we observed the Berezinskii-Kosterlitz-Thouless (BKT) phase transition in monolayer V2XN with the transition temperature TBKT being above room temperature. In particular, monolayer V2AsN has a magnetic anisotropy energy (MAE) of 292.0 μeV per V atom and a TBKT of 434 K, which is larger than that of monolayer V2PN. Moreover, a tensile strain of 5% can further improve the TBKT of monolayer V2XN to be above 500 K. Our results indicated that Janus monolayer V2XN (X = P, As) can be candidate materials to realize high-temperature 2D-XY ferromagnetism for spintronics applications.