Magnetic behaviour of the honeycomb antiferromagnet BaNi₂V₂O₈

Here we present our recent investigations of a spin-1 honeycomb antiferromagnetic BaNi₂V₂O₈ which is a highly 2D antiferromagnet with XY anisotropy making this compound a potential candidate for the Berezinsky-Kosterliz-Thouless topological phase transition. Single crystal inelastic neutron scattering measurements in the honeycomb plane at 4 K reveal that the magnetic excitations extend from 0.3-26 meV and consist of two anisotropy-split gapped modes with gaps of 0.3 meV and 3.3 meV arising from the anisotropy within the a-b plane and XY anisotropy respectively. The excitations agree well with simulations based on linear spin - wave theory and are completely dispersionless in the out-of-plane direction suggesting negligible interplane coupling in spite of the long range magnetic order below T_N = 48 K. A detailed investigation of the order parameter and correlation length are presented and compared to various theories.