Wildes, A. R.Zhitomirsky, M. E.Ziman, T.Lancon, D.Walker, H. C.2020-07-042020-07-042020-07-042020-06-1410.1063/5.0009114https://infoscience.epfl.ch/handle/20.500.14299/169835WOS:000541081600002FePS3 is a van der Waals compound with a honeycomb lattice that is a good example of a two-dimensional antiferromagnet with Ising-like anisotropy. Neutron spectroscopy data from FePS3 were previously analyzed using a straightforward Heisenberg Hamiltonian with a single-ion anisotropy. The analysis captured most of the elements of the data; however, some significant discrepancies remained. The discrepancies were most obvious at the Brillouin zone boundaries. The data are subsequently reanalyzed, allowing for unequal exchange between nominally equivalent nearest-neighbors, which resolves the discrepancies. The source of the unequal exchange is attributed to a biquadratic exchange term in the Hamiltonian, which most probably arises from a strong magnetolattice coupling. The new parameters show that there are features consistent with Dirac magnon nodal lines along certain Brillouin zone boundaries.Physics, AppliedPhysicsmagnetic ordertransitionmodelmnfetext::journal::journal article::research article