Generalized anisotropic spin Hamiltonian for NiPS₃: spin-flop transition and dipole interaction

Two-dimensional (2D) van der Waals (vdW) magnets have attracted considerable attention owing to their fascinating property and promising applicability. NiPS₃ has become a focus of recent research interest by displaying several unusual phenomena such as coherent many-body exciton condensation and highly anisotropic magneto-optical behavior. However, the generalized spin Hamiltonian relevant to this material is yet to be established, while NiPS₃ was considered as a realizing 2D XY- or XXZ- model, which is incapable of entirely elucidating the experimental anisotropic natures of such materials. Furthermore, recent experiments have seen the characteristic behaviors related to a spin-flop transition which is crucially determined by magnetic anisotropy. In this study, we use torque magnetometer and density functional theory to construct a general spin Hamiltonian of NiPS₃. Our investigations clearly show a spin-flop transition which is described by our spin Hamiltonian. Our results indicate that the magnetic anisotropic energy order principally originates from magnetic dipole-dipole interactions. Our results demonstrate the merits of magnetic vdW materials and related systems for the pursuit of spintronic or magnetic device functionalities.