Control of the multiferroic transition in Ni3V2

We have studied the effects of doping magnetic ions on the phase transitions in polycrystalline Ni${}_{3}$V${}_{2}$O${}_{8}$ 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 Co${}_{3}$V${}_{2}$O${}_{8}$ are suppressed rapidly with Ni doping. We present phase diagrams for (Ni${}_{1\ensuremath{-}x}$M${}_{x}$)${}_{3}$V${}_{2}$O${}_{8}$ (M = Cu and Co). These studies suggest that the spin structures in Ni${}_{3}$V${}_{2}$O${}_{8}$ 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.