Multiferroic properties of polyvinyledene fluoride/nickel nano-composites

Abstract

Electrical and magnetic properties of ferroelectric polymer (polyvinyledene fluoride) and ferromagnetic metal [nanocrystalline nickel (nc-Ni)] composites have been investigated as a function of volume fractions of nc-Ni (f_Ni). A significant enhancement in saturation magnetization of 24 emu/g, measure of permeability (μ') of 1.11 and dielectric constant of 2050 at 100 Hz has been observed at the electrical percolation threshold (f_c) of the composite. The critical exponents (x and y) obtained are within the universal regime. The decrease of magnetization of the composite with decrease in f_Ni is attributed to the dilution effect and magnetic dipolar exchange interaction. The constancy of coercive field (H_c) has been explained on the basis of Stoner-Wohlfarth model. The value of μ' increases linearly with increase of f_Ni as the magnetic flux concentrates over individual n_c-Ni clusters/particles even beyond f_c. On the other hand, the value of μ' decreases for pure n_c-Ni probably due to the increased connectivity among the n_c-Ni clusters/particles and hence being a conductor results in eddy current generation in alternating magnetic field. The enhancement of dielectric constant near f_c is explained with the help of boundary layer capacitor effect.