No abstract

A series of Li–Zn mixed ferrites with composition formula Li0.5–0.5xZnxFe2.5–0.5xO4 is prepared by the solid‐state reaction method. The variation of lattice parameter with composition is explained on the basis of tetrahedral ionic radius. Thermopower studies are undertaken over a temperature range 300 to 750 K by the differential method. From the Seebeck coefficient S, the values of charge carrier concentration n and mobility μe are computed. The values of n are found to decrease while those of μe are increasing continuously with increasing temperature. On the basis of these results, a mechanism for the conduction in Li–Zn ferrites is suggested.

Dielectric measurements of cobalt substituted W-type barium–zinc hexagonal ferrites are undertaken both as a function of frequency and temperature. The dielectric constant is found to decrease continuously with increasing frequency while it increases continuously with increasing temperature. The variation of dielectric constant with dopants concentration is explained on the basis of magnetic cation orientation. From the temperature variation of dielectric constant two transitions, one due to the spin reorientation in the temperature range 450–500 K and the other one due to a ferri to paramagnetic transition have been observed. Suitable explanations for the observed behavior are given.

Thermopower and electrical conductivity studies of copper substituted Mg‐Al ferrites are undertaken over the temperature range 300 to 700 K. On the basis of the sign of the Seebeck coefficient (S), the ferrites under study can be considered as n‐type semiconductors. A model is arrived at using Seebeck coefficient data to evaluate the charge carrier concentration. The temperature variation of Seebeck coefficient, carrier concentration (n), and mobility (m̈e) is also discussed. Using the data a conduction mechanism is suggested.

Thermopower studies of some cobalt-substituted BaZn-W-type hexagonal ferrites are undertaken as a function of composition and temperature over a temperature range 300 to 800 K. On the basis of the sign of the Seebeck coefficient, the ferrites under study are classified as n-type semiconductors. From the temperature variation of Seebeck coefficient a transition due to the reorientation of spins around 475 K has been noticed. Assuming that the conduction in W-type ferrites is predominantly due to the hopping of electrons between Fe2+ and Fe3+ ions of the spinel block, a mechanism to explain the phenomenon of charge transport in these ferrites is suggested.