Control of the multiferroic transition in Ni3V2O8 by transition metal doping

We have studied the effects of doping magnetic ions on the phase transitions in polycrystalline Ni3V2O8 samples using magnetic, dielectric, and specific heat measurements. Substituting spin-1/2 Cu results in a larger suppression of the transition temperatures than observed on doping with spin-3/2 Co. The multiferroic-ordering transition persists at small concentrations for both Co and Cu dopants, with this phase still developing at concentrations of almost 30 at% Co. However, the multiferroic-magnetic structure is completely suppressed at only 10 at% Cu. On the Co-rich side of the composition, we find that the magnetic-ordering temperatures for Co3V2O8 are suppressed rapidly with Ni doping. We present phase diagrams for (Ni1-xMx)(3)V2O8 (M = Cu and Co). These studies suggest that the spin structures in Ni3V2O8 responsible for the development of ferroelectric order are relatively robust against perturbations produced by magnetic dopants, with the most significant disruption of the magnetic structure developing for Cu doping.