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Cation distribution, hyperfine parameters and conduction mechanism in the ferrimagnetic system Cu 0.5 Co 0.5 Ga x Fe 2– x O 4
Author(s) -
AtaAllah S. S.,
Kaiser M.
Publication year - 2005
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.200440012
Subject(s) - polaron , hyperfine structure , spinel , ferrimagnetism , octahedron , analytical chemistry (journal) , materials science , electrical resistivity and conductivity , content (measure theory) , ion , lattice constant , chemistry , crystallography , diffraction , crystal structure , magnetization , magnetic field , physics , optics , atomic physics , organic chemistry , quantum mechanics , chromatography , metallurgy , electron , mathematical analysis , mathematics
Compositions having the chemical formula Cu 0.5 Co 0.5 Ga x Fe 2– x O 4 with (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 Fe 3+ 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 at x > 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 exponent s with 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 temperature T C of these samples is found to decrease linearly with increasing Ga content x . 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)