Dielectric and magnetic properties of ZnO-doped cobalt ferrite

A series of cobalt ferrites with the chemical composition Co1+xZnxFe2-2xO4 (x = 0.0, 0.1, 0.2, 0.4) were obtained by a conventional ceramic method. The ZnO-doped samples have a smaller lattice constant than that of CoFe2O4 by adjusting part of the cobalt ions to the octahedral sites. Doping with ZnO could greatly improve the dielectric and magnetic properties. AC dielectric properties show that the samples had semiconductor characteristics for an electron exchange between ions with a different chemical valence. The dielectric constant of the ZnO-doped ferrites is mainly enhanced by Maxwell-Wagner polarization and a Koops mechanism. In comparison with pure CoFe2O4, the sample with small amounts of ZnO-doping has a higher permeability and a much lower coercivity with the condition of a small decrease in magnetization saturation, and it shows an obvious magnetostrictive effect at a magnetic field of <60 mT while the pure cobalt ferrite sample does not, although the saturated magnetostriction decreases. These results indicate that ZnO doping improves the magnetostrictive sensitivity of cobalt ferrites.