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Co x Fe 3 − x O 4 -based (x=0.05–1.6) nanoparticles prepared by combustion reaction were investigated using x-ray diffraction, Raman spectroscopy, and Mössbauer spectroscopy. The Mössbauer data revealed Co2+ in both tetrahedral (site A) and octahedral (site B) sites of the cubic ferrite structure. For x⩽0.4 the experimental data indicated the synthesis of a core-shell structure, with hematite as the shell and cobalt ferrite as the core of the nanoparticle. Differences in crystalline structure between the two phases support the evidences we found of a highly stressed core-shell interface, leading to symmetry reduction of the tetrahedral and octahedral sites.

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Samples of ZnxMg1−xFe2O4 (0≤x≤1) synthesized by the combustion reaction method were investigated by x-ray diffraction, Mössbauer spectroscopy, and Raman spectroscopy. All the samples are found to have a cubic spinel structure and the lattice parameter increases linearly with increasing Zn-content (x). The Mössbauer data showed that the replacement of Mg2+ ions for Zn2+ ions changes substantially the hyperfine parameter. Moreover, it was verified the presence of Fe3+ ions both in A and B sites. The Raman spectra showed five predicted Raman bands for the spinel structure and it was observed the splitting of the A1g Raman mode into tree branches, where each one have been attributed to peaks belonging to each ion (Zn, Mg, and Fe) in the tetrahedral positions.

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