Magnetic structure and magnon dynamics of the quasi-two-dimensional antiferromagnet<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>FePS</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>

Neutron scattering from single crystals has been used to determine the magnetic structure and magnon dynamics of ${\text{FePS}}_{3}$, 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 ${\mathbf{k}}_{M}=\left[01\frac{1}{2}\right]$ 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 ${J}_{1}=1.46, {J}_{2}=\ensuremath{-}0.04$, and ${J}_{3}=\ensuremath{-}0.96$ meV. The single-ion anisotropy is large, $\mathrm{\ensuremath{\Delta}}=2.66$ meV, explaining the Ising-like behavior of the magnetism in the compound. The interlayer exchange is very small, ${J}^{\ensuremath{'}}=\ensuremath{-}0.0073$ meV, proving that ${\text{FePS}}_{3}$ is a very good approximation to a two-dimensional magnet.

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