Incommensurability and spin dynamics in the low-temperature phases of Ni3V2O8

Abstract

Magnetic order and low-energy spin dynamics in the zero field ground state of Ni3V2O8 are revealed in elastic and inelastic neutron scattering experiments. Neutron diffraction shows that below T=2.3 K the Ni2+ moments (spin S=1) order in a cycloid pattern with incommensurate wave vector kICM=(0,1,τ), where τ=0.4030±0.0004, which is superimposed on a commensurate antiferromagnetic spin arrangement with kCM=(0,0,0). Three spin wave modes are discerned below E∼3 meV in inelastic measurements and qualitatively described by a model Hamiltonian that involves near neighbor exchange, local anisotropy, and a small biquadratic coupling between the spine and cross-tie sites. Results from both elastic and inelastic scattering experiments suggest that the two sublattices on spine and cross-tie sites are largely decoupled. © 2013 American Physical Society.