Complex permittivity and permeability dependence of Ba4Zn2−ZCoZFe36O60 U-type hexaferrites prepared by citrate sol–gel on composition, annealing temperature and frequency

The present paper deals with the investigations of the preparation of hexaferrites with Z=0.0, 0.5, 1.0, 1.5, 2.0 by citrate sol–gel process as well as the complex dielectric constant and complex permeability as functions of measuring frequency from 100 MHz to 6 GHz, annealing temperature and composition. The results show that the real part of permeability decreased with frequency increasing for all samples annealed at 1000–1200 °C but Co2U ferrite (Ba4Co2Fe36O60). The natural resonance phenomenon is observed in μ″ spectrum for all hexaferrites with exception for Co2U. The natural resonance frequency is a function of annealing temperature as well as composition, which shifts to lower frequency with Zinc content and increasing calcaining temperature.