Spin wave dispersion of the van der Waals antiferromagnet NiPS3

We calculate the magnon dispersion spectra of the two-dimensional zigzag van der Waals antiferromagnet NiPS3 for monolayer, bilayer, and bulk systems as a function of an external magnetic field. We compare the exchange and anisotropy constants of a spin model as calculated by first principles with those obtained experimentally. We can accurately explain the transition from a collinear to a canted ground state for a magnetic field applied normal to the (in-plane) easy-axis and a spin-flop transition when the field is parallel to it. A topologically protected Dirac nodal line is present and robust with respect to both external and anisotropy fields.