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In this work, the comparative study on the electrical transport properties of nanocrystalline nickel ferrite (NiFe2O4) and its bulk counterpart has been carried out in detail by using complex impedance spectroscopy in a wide range of frequencies (100 Hz-1MHz) and temperatures (40°C-320°C).The dispersive nature of the dielectric constant and loss factor is explained by the Maxwell-Wagner model and Koop’s phenomenological theory. The value of the dielectric constant for nanocrystalline nickel ferrite is found to be more as compared to its bulk counterpart. The frequency variation dielectric permittivity is well fitted with the modified Debye formula, which suggests the presence of multiple relaxation processes. The temperature dependent ac conductivity follows Jonscher’s universal power law and reveals the presence of multiple transport mechanisms from small polaron hopping (SPH) to correlated barrier hopping (CBH) mechanism near 200°C.The estimated values of Mott parameters are found to be satisfactory. Thermally activated relaxation phenomena have been confirmed by scaling curves of imaginary impedance (Z") and modulus (M"). The comparison between the Z" and M" spectra indicates that both long-range and short-range movement of charge carriers contribute to dielectric relaxation with short-range charge carriers predominating at low temperatures while long-range charge carriers are dominating at high temperatures. Analysis of the semicircular arcs of Nyquist plot indicates the presence of grain boundary contribution to the electrical conduction process for the nanocrystalline sample at high temperatures. The non-Debye type of relaxation has been examined by stretching exponential factor (β) which has been estimated by fitting the modified KWW (Kohlrausch-Williams-Watts) equation to the imaginary electric modulus curve. The value of β is found to be strongly temperature dependent and its value for the nanocrystalline sample is less than that of the bulk system which is explained on the basis of dipole-dipole interaction.

Lead Zirconate Titanate [Pb(Zr0.52Ti0.48)O3/PZT] and Cobalt Ferrite [CoFe2O4/CFO] based multiferroic composites [(1-x)PZT-(x)CFO] with (x = 0.10–0.40) have been prepared to study its magnetoelectric (ME) and multiferroic properties. X-ray diffraction method along with the Rietveld refinement technique reveals that the crystal symmetries corresponding to PZT and CFO exist independently in the composites. The effect of interfacial strain on lattice distortion in PZT has been observed. It is well correlated with the magnetoelectric coupling of the composites. Dispersion behavior of dielectric constant with frequency can be explained by the modified Debye model. Different relaxation phenomena have been observed in PZT-CFO particulate composites. The ferroelectric properties of composites decrease with the increase in percentage of CFO in the composite. Both saturation (Ms) and remanent (Mr) magnetization increase with the increase in CFO content in the composite. The maximum ME coupling was found to be 1.339 pC/cm2 Oe for the composition (0.80) PZT-(0.20) CFO at the application of maximum magnetic field of 50 Oe. The multiferroic properties in CFO-PZT can be explained by the lattice strain at the CFO-PZT interfaces.

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