Cation distribution, hyperfine parameters and conduction mechanism in the ferrimagnetic system Cu0.5Co0.5GaxFe2–xO4

Abstract

AbstractCompositions having the chemical formula Cu0.5Co0.5GaxFe2–xO4with (0.0 ≤x≤ 0.5) have been prepared by the usual ceramic processing from high‐purity oxides. X‐ray diffraction measurements are used for analyzing the composition, lattice parameter, density, porosity and grain size of these compounds. The area ratio of Fe3+at the tetrahedral A‐ and octahedral B‐sites deduced from the spectral analysis of Mössbauer measurements on the present spinel system gives evidence that Ga replaces Fe at A‐site in the range 0.0 <x≤ 0.3. As the Ga content increases (x> 0.3), it replaces Fe at B‐site. This change in the site preference reflects an abrupt change in the hyperfine parameters with Ga content atx> 0.3. The electrical measurements as a function of temperature and frequency on these materials revealed semiconducting behavior. These results show a significant increase in the frequency dependence of conductivity as Ga content increases. Variation of the universal exponentswith temperature indicates the presence of small‐polaron (SP) hopping mechanism at low Ga content. As Ga substitution progressed, the overlap large polaron (OLP) becomes the predominant hopping mechanism in these compounds. The determined transition temperatureTCof these samples is found to decrease linearly with increasing Ga contentx. The results obtained in this study are interpreted in light of the cation–cation and cation–anion–cation interactions in the spinel structure. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)