Dielectric relaxation, conductivity behavior and magnetic properties of Mg substituted Zn-Li ferrites

Spinel ferrites having compositions Zn0.5Li1-2xMgxFe2O4 (0 <= x <= 0.5) have been prepared by sol-gel auto combustion technique. The dielectric properties of these ferrites have been studied using impedance measurements in the frequency range 10 Hz-10 MHz and in the temperature range 310-473 K. The effect of temperature, frequency and composition on dielectric constant (is an element of'), dielectric loss (tan delta) and conductivity (sigma) have been discussed in terms of hopping of charge carriers (Fe2(+1) <-> Fe3+). The occurrence of peak in the dielectric loss (tans) spectra is found to be temperature and composition dependent. The electrical modulus formulism has also been employed to study the relaxation dynamics of charge carriers and the results indicate the presence of non-Debye type of relaxation in these ferrites. Identical values of activation energy for dc conduction (E-dc) and for conductivity relaxation (E-M") reveal that the charge carriers have to overcome the same energy barrier while conducting and relaxing. A single 'master curve' for normalized plots of all the modulus isotherms observed for a given composition indicates the temperature independence of dynamical process for charge carriers in the present ferrites. The absence of hysteresis and non-attainment of saturation magnetization (even at 8 kOe) suggests the super paramagnetic behaviour of these ferrites. (C) 2010 Elsevier B.V. All rights reserved.