Magnetically induced ferroelectricity in the buckled Kagome antiferromagnet Ni3V2O8

Ni3V2O8 is one of several recently identified multiferroic materials in which ferroelectricity is produced by long-range magnetic order. This staircase Kagome compound adopts a sequence of distinct low temperature magnetic phases, which exhibit different optical, dielectric, and transport properties, most notably ferroelectric order arising from a polar incommensurate magnetic structure. We give an overview of the experimental results from the existing literature on Ni3V2O8, and briefly discuss models that describe the coupling between magnetic and ferroelectric properties. We show that the temperature dependence of the dielectric constant provides evidence for spin-charge coupling in Ni3V2O8 away from the ferroelectric phase. An anomaly in the thermal conductivity at the incommensurate-commensurate phase transition suggests that spin scattering may limit thermal transport in the incommensurate phase. We associate each of the two incommensurate phase transitions with one magnetic order parameter, and we show that the temperature dependence of the ferroelectric polarization closely follows the product of these two magnetic order parameters-corroborating the validity of the phenomenological trilinear coupling model. Finally, we present inelastic powder neutron scattering measurements that provide evidence of several weakly dispersive magnetic modes that are typical for strongly frustrated antiferromagnets with large spin anisotropies.