Mossbauer and magnetic studies of Mg1+2xSbxFe2-3xO4 spinel ferrites

Spinel-related Mg1+2xSbxFe2-3xO4 samples (x = 0.0, 0.05, 0.10, 0.15, 0.20, and 0.30) prepared using the conventional double sintering technique were investigated using Fe-57 Mossbauer spectroscopy and magnetic measurements. Mossbauer spectra favor a cationic distribution of the form (Mg delta Fe1-delta)(A)[Mg1-2x -delta SbxFe1+delta-3x]O-B(4) among the tetrahedral-A and octahedral-B sites of the spinel structure. The cation distribution parameter (delta) was found to vary with the Sb5+ concentration (x). The Mossbauer hyperfine magnetic fields at both sites and the Curie temperatures of the ferrites decrease as x increases. This was attributed to gradual weakening in the magnetic exchange interaction as more Fe3+ ions are substituted by diamagnetic Sb5+ and Mg2+ ones. The sample with x = 0.30 exhibits short range magnetic order due to cationic clustering and/or superparamagnetism. The magnetization of all samples was found to be temperature-dependent implying that 6 depends on temperature in addition to x. At low temperatures the substituted ferrites (x not equal 0.0) unexpectedly exhibit higher magnetization values relative to that of the pure ferrite MgFe2O4. This behavior, while at variance with the Neel's model for ferrimagnetism, is explicable in terms of the spin canting mechanism proposed in the Yafet-Kittel model. (C) 2013 Elsevier B.V. All rights reserved.