Themodern human society made their need of small size, lightweight, portable, flexible and reliable devices with high battery back up along with fast charging and minimal heat dissipation which could support for long life of the devices. That requires a good dielectric material with understanding of their electrical transport property. Electrical conductivityis basically due to the bound charge carrier and/or free charge carriers. Cobalt ferrite is a hard ferrimagnetic material which exhibits unique properties high Curie temperature, high coercivity, high magneto-crystalline anisotropy, moderate saturation magnetization, high dielectric permittivity, low eddy current losses, dielectric losses, good mechanical hardness, and chemical stability. These unique properties make it useful for development of microwave and spintronic devices, solar cells, magnetostrictive sensors, drug delivery, transducers, actuators, Li batteries, super capacitors, and memory devices, etc. Because of this unique feature, recently metal ion substitution for Fe3+/Co2+ ions in spinel ferrite gaining importance for utilization in high charge storage device as dielectric material in capacitors and battery applications. It is important to note that these materials exhibit both free and bound charges. Hence, its electrical properties became complicated because it depends upon different factors (i.e. method of preparation, crystallite size, substitution element etc.). Hence, it is necessary to understand bound as well as free electron transport of nanocrystalline spinel ferrite for technological applications. It is interesting to note that, there is an important correlation exists between bound charge and free charge properties on nancrystalline cobalt ferrite. Two transitions takes place in both the temperature depended ac and DC conductivity curve. The transport properties can be understood by employing the different models.

Manoranjan Karwas born in India on 1st June 1975. He had his PhD degree in Physicsfrom Indian Institute of Technology Guwahati in December 2004. He worked as researcher at Centre for Nanotechnology in the same institute. He is working as a faculty member at the department of Physics, Indian Institute of technology Patna since December 2008. He is a specialist in synthesis of nanoparticle and its composites. He is an expert on the crystal structure, electrical transport and magnetic properties of nanomaterials.