High frequency dielectric behaviour of aluminium-substituted lithium ferrites

The dielectric constant (epsilon') and complex dielectric constant (epsilon ") of aluminium-substituted lithium ferrites have been measured at room tem perature in the high frequency range of 100 kHz to 1 MHz. The values of die lectric lass tangent (tan delta) have been computed from epsilon' and epsil on". Plots of dielectric constant (epsilon') vs, frequency show a normal di electric behaviour of the spinel ferrites. The frequency dependence of the dielectric loss tangent (tan delta) is found to be abnormal, giving a peak at a certain frequency for all the ferrites under investigation. A qualitat ive explanation is given for the composition and frequency dependence of th e dielectric constant and dielectric loss tangent. The dielectric constant for these mixed ferrites is approximately inversely proportional to the squ are root of the resistivity. A plot of dielectric constant vs. temperature shows a transition near the Curie temperature. An attempt is made to explai n the possible mechanism for this observation. (C) 2000 Elsevier Science B. V. All rights reserved.