Magnetic structure and magnon dynamics of the quasi-two-dimensional antiferromagnet FePS3

Neutron scattering from single crystals has been used to determine the magnetic structure and magnon dynamics of FePS3, an S = 2 Ising-like quasi-two-dimensional antiferromagnet with a honeycomb lattice. The magnetic structure has been confirmed to have a magnetic propagation vector of k(M) = [01 1/2] and the moments are collinear with the normal to the ab planes. The magnon data could be modeled using a Heisenberg Hamiltonian with a single-ion anisotropy. Magnetic interactions up to the third in-plane nearest neighbor needed to be included for a suitable fit. The best fit parameters for the in-plane exchange interactions were J(1) = 1.46, J(2) = -0.04, and J(3) = -0.96 meV. The single-ion anisotropy is large, Delta = 2.66 meV, explaining the Ising-like behavior of the magnetism in the compound. The interlayer exchange is very small, J' = -0.0073 meV, proving that FePS3 is a very good approximation to a two-dimensional magnet.