Size effect on electrical and magnetic properties of mechanically alloyed CoFe₂O₄ nanoferrite

Highly crystalline cobalt ferrite (CoFe₂O₄) nanoparticles with diameter ranging from 5 to 19 nm were prepared by a mechanical alloying method followed by thermal treatment. The formation of a single-phase compound was confirmed by basic X-ray structural analysis, and the nano-structure of the sample was confirmed by high-resolution transmission microscope. The crystallite size of the material was found to be milling time dependent. Relative permittivity and tangent loss of the material are strongly dependent on the crystallite size. The temperature-frequency dependence of dielectric parameters and temperature dependent electrical conductivity has successfully been explained using Maxwell–Wagner and Koop’s phenomenological models. Impedance spectroscopy clearly explains dependence of resistive characteristics and dielectric relaxation of the material. The nature of impedance spectra exhibits a typical negative-temperature-co-efficient of resistance. The magnetic measurement shows that saturation magnetization is particle size dependent. The ac conductivity spectrum of the material shows a typical-signature of an ionic conduction, and is found to obey Jonscher’s universal power law. The change in activation energy with particle size is observed suggesting a typical conduction mechanism in the material.