Spin wave spectra of single crystal CoPS$_3$

TL;DR

This study measures and models the spin wave spectra of single-crystal CoPS$_3$, revealing multiple energy gaps and complex exchange interactions, advancing understanding of layered van der Waals antiferromagnets.

Contribution

It provides a detailed linear spin wave model for CoPS$_3$, including exchange interactions up to third nearest neighbors and anisotropy parameters, which was not previously established.

Findings

Four distinct spin wave branches observed.

Large energy gaps indicate significant anisotropy.

Exchange interactions include ferromagnetic and antiferromagnetic couplings.

Abstract

The spin waves in single crystals of the layered van der Waals antiferromagnet CoPS$_3$ have been measured using inelastic neutron scattering. The data show four distinct spin wave branches with large ($\gtrsim 14$ meV) energy gaps at the Brillouin zone center indicating significant anisotropy. The data were modelled using linear spin wave theory derived from a Heisenberg Hamiltonian. Exchange interactions up to the third nearest-neighbour in the layered planes were required to fit the data with ferromagnetic $J_1 = -1.37$ meV between first neighbours, antiferromagnetic $J_3 = 3.0$ meV between third neighbours, and a very small $J_2 = 0.09$ meV between second neighbours. A biaxial single-ion anisotropy was required, with a collinear term $D^x = -0.77$ meV for the axis parallel to the aligned moment direction and a coplanar term $D^z=6.07$ meV for an axis approximately normal to the layered crystal planes.