Spin waves in the ferromagnetic ground state of the kagome staircase system Co₃V₂O₈

Inelastic neutron-scattering measurements were performed on single-crystal Co₃V₂O₈ wherein magnetic cobalt ions reside on distinct spine and cross-tie sites within kagome staircase planes. This system displays a rich magnetic phase diagram which culminates in a ferromagnetic ground state below T_C∼6 K. We have studied the low-lying magnetic excitations in this phase within the kagome plane. Despite the complexity of the system at higher temperatures, linear spin-wave theory describes most of the quantitative detail of the inelastic neutron measurements. Our results show two spin-wave branches, the higher energy of which displays finite spin-wave lifetimes well below T_C, and that, surprisingly, the magnetic exchange coupling between Co moments on the spine sites is negligible.