Two-dimensional XY ferromagnetism above room temperature in Janus monolayer V 2 XN (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 V 2 XN (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 V 2 XN. With the help of the Monte Carlo simulations, we observed the Berezinskii-Kosterlitz-Thouless (BKT) phase transition in monolayer V 2 XN with the transition temperature T BKT being above room temperature. In particular, monolayer V 2 AsN has a magnetic anisotropy energy (MAE) of 292.0 μeV per V atom and a T BKT of 434 K, which is larger than that of monolayer V 2 PN. Moreover, a tensile strain of 5% can further improve the T BKT of monolayer V 2 XN to be above 500 K. Our results indicated that Janus monolayer V 2 XN (X = P, As) can be candidate materials to realize high-temperature 2D-XY ferromagnetism for spintronics applications.