Enhancement of electrical and dielectric properties of Cr doped BaZn2 W-type hexaferrite for potential applications in high frequency devices

Nanocrystalline W-type hexaferrites of nominal stoichiometry of BaZn2CrxFe16-xO27 (x <= 1) have been synthesized by the chemical co-precipitation method and their structural, electrical and magnetic properties have been investigated. In most of the published work, synthesis of a single W-type hexagonal phase is reported at high annealing temperatures of 1300-1573 K. However, we have attempted to synthesize it at lower annealing temperatures of 1223 K. The X-ray diffraction (XRD) patterns conform to the standard single phase of the hexagonal W-type structure. The elemental composition estimated from the energy dispersive X-ray fluorescence (ED-XRF) analysis is in good agreement with the nominal composition. Surface morphological studies are carried out using scanning electron microscopy (SEM) analysis. The DC electrical resistivity (rho) and AC magnetic susceptibility (chi) studies are performed in a temperature range of 300-663 K and 423-663 K, respectively. We are able to enhance the room temperature resistivity (rho(RT)) of BaZn2Fe16O27 by doping it with Cr to the order of 10(9) Omega cm which is higher than those previously reported for the W-type hexaferrites (10(3)-10(7) Omega cm). The dielectric constant (epsilon') and dielectric loss (tan delta) decrease with the frequency, on the other hand both these parameters are enhanced by doping the material with Cr. The enhancements in the above mentioned parameters make them promising for use at high frequencies in order to reduce eddy current losses, in radar absorbing purposes and for electromagnetic interference attenuation. All the samples show a metal to semiconductor transition at a temperature (TM-S) that varies with chromium concentration. Dielectric studies show that the electrical conduction in these materials is due to the collective contribution of electrons as well as of the holes. (C) 2008 Elsevier B.V. All rights reserved.