The magnon dynamics and spin exchange parameters of FePS3

The spin waves in a powdered sample of a quasi-two-dimensional antiferromagnet, FePS3, have been measured using neutron inelastic scattering. The data could be modelled and the exchange interactions determined using a two-dimensional Heisenberg Hamiltonian with single ion anisotropy. A suitable fit to the data could only be achieved by including magnetic interactions up to the third nearest neighbour, which is consistent with the findings for other members of the MPS3 family (M=transition metal). The best fit parameters at 6 K were J1 = 1.49 meV, J2 = 0.04 meV, J3 =− 0.6 meV, with an anisotropy of Δ = 3.7 meV. Measurements as a function of temperature give a coarse measure of the behaviour of the anisotropy and the nature of the phase transition.