Multiferroic properties of polyvinyledene fluoride/nickel nano-composites
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 (fNi). 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 (fc) 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 fNi is attributed to the dilution effect and magnetic dipolar exchange interaction. The constancy of coercive field (Hc) has been explained on the basis of Stoner-Wohlfarth model. The value of μ' increases linearly with increase of fNi as the magnetic flux concentrates over individual nc-Ni clusters/particles even beyond fc. On the other hand, the value of μ' decreases for pure nc-Ni probably due to the increased connectivity among the nc-Ni clusters/particles and hence being a conductor results in eddy current generation in alternating magnetic field. The enhancement of dielectric constant near fc is explained with the help of boundary layer capacitor effect.
Composite materials; Percolation; Critical exponent; Permeability; Multiferroic
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