Contribution to Analysis of Co/Cu Substituted Ni-Zn Ferrites

In this communication, Co/Cu substituted Ni-Zn ferrites processed through sol-gel synthesis using polyethylene glycol (PEG) as a chelating agent are studied, intending to aid in understanding and choosing the optimum ferrite material for high frequency applications. Lattice constant and average crystallite size have been estimated from FWHM of the X-ray diffraction peaks, and these parameters are understood by considering the ionic radii of the substituted as well as the replacing ions. Observed variations in saturation magnetization and initial permeability for these ferrites have been explained on the basis of anisotropy contribution for cobalt and segregation of copper at grain boundaries evident from scanning electron micrographs. 1. Introduction The increasing demand for ferrite materials for core applications having reduced size, weight, and cost necessitates to develop ferrites containing ultrafine particles with improved efficiency at high frequencies. Ferrites show interesting magnetic and electronic properties as the particle size decreases compared with those of the bulk ferrites. The extensive study on mixed ferrite systems reveals that Ni-Zn ferrites are well-known core materials suitable for high frequency applications up to 100？MHz due to their high value of saturation magnetization, moderate permeability, and high resistivity parameters responsible for low losses [1–4]. Though ultrafine particles provide large grain boundary area to develop resistivity by many folds, expected enhancement in magnetization is hindered by these tiny grains to extend the cooperative effects among the particles. This may be achieved by substitution of a diamagnetic impurity ion in Ni-Zn ferrites which tend to occupy tetrahedral sites or a ferromagnetic impurity having strong preference for octahedral sites of the spinel lattice supposed to be substituted. In case of nanoferrites, inversion of the ion occurs against its natural preference (in bulk ferrites) as reported earlier [3]. By considering this argument, in this communication, Cu/Co ions have been substituted, replacing nickel ions in sol-gel synthesized Ni-Zn ferrites using polyethylene glycol. PEG serves as a chelating agent in controlling the crystallite size by arresting the particles in the polymer matrix and facilitates homogeneous dispersion of ferrite nanoparticles. 2. Experimental Details The method of preparation of samples was described elsewhere [4]. X-ray diffraction (XRD) is used for the identification of the material phases and crystal structure, determination of average crystallite size