Electric and Magnetic Studies on Copper/Cobalt Substituted Ni-Zn Ferrites

Abstract

Lattice constant, DC resistivity and saturation magnetisation measurements on copper or cobalt substituted Ni-Zn ferrites have been reported in this paper. Cobalt has shown predominant impact on saturation magnetisation where as copper exhibited similar impact on DC resistivity for lower concentrations of dopant ions. The variations in both the parameters have been explained on the basis of their respective ionic radii size, ionic distributions, associated conduction mechanisms and contributions of magnetic exchange interactions. Introduction Ferrites find a large number of applications over a wide frequency range due to their higher electrical resistivities and better magnetic properties. The properties of ferrites are highly sensitive to amount of impurities present in or added to them. There have been many reports on ferrites [ 1-41 on the substitution of ions of different valences to improve the required properties depending on the applications of interest. In power electronics, the devices in the design of inductor and transformer cores make extensive use of ferrites such as Mn-Zn and Ni-Zn systems [5]. Particularly, for the operating frequencies in excess of 1 MHz, NiZn ferrites have an edge [6] . The cores for such applications require high magnetisation and low core losses. Improvements in magnetisation and resistivity as a result of compositional modifications would certainly help these materials to be used as more compact devices in application systems. The present paper reports the variations of lattice constant, DC resistivity and saturation magnetisation of NiZn ferrites doped with ferromagnetic cobalt or diamagnetic copper and discusses the results in terms of conduction processes and magnetic interactions between the cations. Ionic distribution for both the systems has been suggested in the light of the knowledge of site preferences of various cations present. Experimental Details Polycrystalline Ni-Zn ferrites with the chemical formula Ni0.35 Zn0.65.~ Me, Fez 0 4 where Me being Cu or Co and x values ranging from 0.00 to 0.25 in steps of 0.05 have been prepared by conventional ceramic technique using the procedure described elsewhere [7]. Calcination and sintering of the samples have been carried out at 975OC and 1250°C respectively for 4 hours in air atmosphere followed by natural cooling. X-ray diffraction patterns confirm single phase cubic spinel structure in all the samples. Characterization of the samples was done further by comparing the measured values of lattice constant and Curie temperature of the basic composition with the respective parameters of the same composition reported earlier and these are found to be in good agreement with each other [7]. DC resistivity measurements on the samples have been made by standard two probe method and saturation magnetisation measurements are made using a VSM with fields up to 15 kOe respectively. Sintered density measurements by Archimedes principle are also presented to understand the impact of substitutions of copper and cobalt in these systems. Results & Discussion The observed sintered densities along with lattice constants for both the Cu and Co doped ferrites