M. Chaitanya Varma

EFFECT OF PARTICLE SIZE ON SATURATION MAGNETIZATION AND MAGNETIC ANISOTROPY OF Ni0.65Zn0.35Fe2O4 NANOPARTICLES

Ni0.65Zn0.35Fe2O4 nanoparticles synthesized by sol–gel process have been subjected to various annealing temperatures with a view of obtaining size dependent properties and critical length. X-ray diffraction, transmission electron microscopy, VSM and ESR experiments were carried out as a function of crystallite size. From the ESR spectra it has been observed that the sample annealed at 1025°C has least magnetic anisotropy. The observed variations in saturation magnetization and coercive field have been explained in terms of magnetic anisotropy.

ENHANCED MAGNETIZATION IN COBALT SUBSTITUTED Ni–Zn NANOFERRITES

Cobalt substituted nickel zinc ferrite nanoparticles (Ni0.65–xCoxZn0.35Fe2.0O4) X varying from 0.0 to 0.65 in steps of 0.15 have been produced using sol–gel method, with PVA as chelating agent. The phase formation of the sintered ferrite was confirmed by X-ray diffraction studies. The lattice parameter a(A°) has been calculated using Nelson–Riley method. The crystallite size has been estimated by the Williamson–Hall method using the full width at half-maximum (FWHM) of the line broadening of all the peaks. Mossbauer spectroscopy (MS) of the samples showed the clear presence of two sextets and distribution of iron over the two sites has been given. Increase in saturation magnetization with cobalt concentration with a slight decrease for x = 0.15 has been observed with the vibrating sample magnetometry study. The observed value of magnetization for Ni0.65Zn0.35Fe2O4 with a particle size of 43.5 nm has been 71 emu/gm at room temperature, which is higher than that reported for samples prepared using chemical methods of the same composition. The results have been explained on the basis of the particle size and cation distribution among various sites.

Estimating the Cation Distributions in Ferrites Using X-Ray, FT-IR, and Magnetization Measurements

The fundamental requirements for the shift of critical frequency to microwave frequencies are smaller grains with single domain, high resistivity, high saturation magnetization, moderate permeability, moderate magnetic anisotropy, and low spin relaxation time. With these guidelines an attempt to produce high performance ferrite for high frequency applications the present work aimed to synthesize cobalt substituted Ni-Zn ferrites using sol-gel method. Investigation of effects of cobalt on crystallite size, saturation magnetization, initial permeability, magnetic anisotropy, and spin relaxation time reveals the suitability of these materials for high frequency applications. Further in this paper cat ion distribution was proposed from the basis of variations in these properties. The results of this paper are thus useful to tailor the properties apt for high frequency applications.

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.