FREQUENCY-DEPENDENCE OF THE COMPLEX IMPEDANCES AND DIELECTRIC BEHAVIOR OF SOME MG-ZN FERRITES

Complex impedances of some magnesium-zinc ferrites, MgxZn1-xFe2O4 (x = 0.4, 0.5, 0.6 and 0.7), in the frequency range of 1 mHz-10 MHz were m easured at 300 K. The complex-plane impedance spectrum from each sampl e indicates that the capacitive and the resistive properties of the ma terials are mainly attributed to the processes that associated with th e bulk (grain) and the grain boundary. A low-frequency dispersion (LFD ) and a negative capacitance regions are also observed at low frequenc ies. A small series resistance of about the same value for all samples is also observed. The bulk and the grain boundary components are anal ysed by assuming a two-layer leaky capacitor. The simulated complex im pedances using the Cole-Cole expression are in agreement with the meas ured values. The dielectric properties of the materials are attributed to the interfacial polarization and LFD at low frequencies and the or ientational polarization at high frequencies. These properties result in the dielectric loss which composed of a Debye-like loss peak at hig h frequency end and a strong LFD below 1 Hz. Both regions exhibit univ ersality with regard to the power-law relation between the dielectric loss (epsilon(r) '' or chi '') and frequency as given by epsilon(r) '' proportional to omega(n-1), where n = 0.14 and n = 0.02, respectively . The exponent is marginally negative, n = -0.03, in the region of neg ative capacitance below 3-4 mHz. The variations of the above propertie s and the characteristic parameters for different compositions of the Mg-Zn ferrites are discussed.