High-frequency dielectric behaviour of polycrystalline zinc substituted cobalt ferrites

The dielectric constant (epsilon') and complex dielectric constant (epsilon ") of zinc substituted cobalt ferrites have been measured at room temperat ure in the high frequency range 100 kHz to 1 MHz. The values of dielectric loss tangent (tan delta) have been computed from epsilon' and epsilon " Plo ts of dielectric constant (epsilon') versus frequency show a normal dielect ric behaviour of the spinel ferrites. The frequency dependence of dielectri c loss tangent (tan delta) is found to be abnormal, giving a peak at certai n frequency for all the ferrites under investigation. A qualitative explana tion is given for the composition and frequency dependence of the dielectri c constant and dielectric loss tangent. The dielectric constant for these m ixed ferrites is approximately inversely proportional to the square root of the resistivity. A plot of dielectric constant versus temperature shows a transition near the Curie temperature. An attempt is made to explain the po ssible mechanism for this observation. (C) 1999 Kluwer Academic Publishers.