Magnetic ordering induced ferroelectricity in α-Cu2V2O7 studied through non-magnetic Zn doping

We have studied the magnetic and electronic properties of Cu2-xZnxV2O7 by magnetization, specific heat, and dielectric measurements. X-ray structural analysis shows a Zn-mediated phase transition from the α- to the β-phase beyond a critical Zn concentration of xc = 0.15. While Cu2V2O7 exhibits a canted antiferromagnetism with an associated weak ferromagnetism in the α-phase, the β-phase is purely antiferromagnetic. The spin canting arises due to the Dzyaloshinskii-Moriya exchange interaction in the anti-symmetric α-phase. The temperature dependence of the heat capacity for the sample in the α-phase shows a clear lambda like transition at a temperature where the magnetic susceptibility also displays an anomaly and indicates an onset of long range magnetic ordering. Dielectric properties display a clear anomaly around the magnetic transition temperature in α-Cu2V2O7. The anomaly weakens with the increase in the Zn concentration and disappears at the doping level where α to β phase transition occurs. This confirms the existence of magneto-electric coupling in α-Cu2V2O7 but not in its β-phase. Analysis of the experimental data shows that magneto-electric coupling is non-linear in nature, which is in agreement with the Landau theory of continuous phase transition. So, α-Cu2V2O7 establishes itself as a promising candidate for magnetic multiferroics.