Origin of Magnetoelectric Coupling Effect and Spin Dynamics of Co4Nb2O9

Neutron powder diffraction experiments reveal that Co4Nb2O9 forms a noncollinear in-plane magnetic structure with Co2+ moments lying in the ab plane. Spin wave excitation of this magnet was measured by using inelastic neutron scattering and soundly simulated by a dynamic model involving nearest and next-nearest exchange interactions, in-plane anisotropy and Dzyaloshinskii-Moriya (DM) interaction. It was found that the in-plane magnetic structure of Co4Nb2O9 is attributed to the large in-plane anisotropy while the noncollinearity of spin configuration is determined by the DM interaction. The high magnetoelectric coupling effect of Co4Nb2O9 in fields can be explained from its special in-plane magnetic structure.