Spin wave spectra of single crystal CoPS${}_3$

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.

11 pages, 6 figures, 3 tables