Effect of cobalt substitution on the properties of nickel-copper ferrite

Cobalt-substituted nickel-copper ferrite samples having the chemical formula Ni0.95-xCoxCu0.05Fe2O4, where x varies as 0.01, 0.02 and 0.03, were prepared by the standard double sintering ceramic technique. The formation of the ferrite phase was confirmed by x-ray diffraction (XRD) studies. Resistivity and thermo-emf variation with temperature were studied in the temperature range from room temperature to 773 K as a function of cobalt content. As the cobalt content increases, the resistivity of the ferrites decreases. AC conductivity measurements made in the frequency range 100 Hz-1 MHz show that conduction in these ferrites is due to small polaron hopping. The dielectric constant and loss tangent (tan delta) were measured at room temperature as a function of frequency in the range 20 Hz to 1 MHz. The room-temperature dielectric measurements show dispersion behaviour with increasing frequency. To understand the conduction mechanism, complex impedance measurements were carried out. The variation in saturation magnetization (M-s) with variation of cobalt content is also studied.