Scaling behaviour of magnetic transitions in Ni3V2O8

We have studied phase transitions in multiferroic Ni3V2O8, through dielectric measurements and by investigating the effects of Zn doping. The divergence of the dielectric constant near T-L = 6.4K can be approximately fit by power law behaviour, but exhibits different critical exponents above and below T-L. The two higher temperature magnetic transitions in (Ni1-xZnx)(3)V2O8, are strongly suppressed as the Zn doping fraction x is increased. The rates of the suppression of both T-H and T-L with x are consistent with two-dimensional spin systems, with the suppression of T-H consistent with Ising spins and the suppression of T-L consistent with Heisenberg spins.