High frequency dielectric behaviour of aluminium-substituted lithium ferrites

The dielectric constant ( ε′) and complex dielectric constant ( ε″) of aluminium-substituted lithium ferrites have been measured at room temperature in the high frequency range of 100 kHz to 1 MHz. The values of dielectric loss tangent (tan δ) have been computed from ε′ and ε″. Plots of dielectric constant ( ε′) vs. frequency show a normal dielectric behaviour of the spinel ferrites. The frequency dependence of the dielectric loss tangent (tan δ) is found to be abnormal, giving a peak at a certain frequency for all the ferrites under investigation. A qualitative explanation is given for the composition and frequency dependence of the dielectric constant and dielectric loss tangent. The dielectric constant for these mixed ferrites is approximately inversely proportional to the square root of the resistivity. A plot of dielectric constant vs. temperature shows a transition near the Curie temperature. An attempt is made to explain the possible mechanism for this observation.