A convenient method for the small-scale preparation of some ferrites

Abstract

The ferromagnetic spinels, MnFe₂O₄, CoFe₂O₄ and NiFe₂O₄, were prepared in small amounts by the thermal decomposition of mixtures of pyridine-1-oxide and pyridine complexes of the corresponding metal nitrates. The thermal decomposition of the chosen complexes proceeds through a liquid stage and this helps to ensure that there is a homogeneous product and that there is rapid formation of the spinel structure when residues are heated between 1000 and 1200° C. Thin layers of these spinels may be obtained by using a solution of the metal complexes in ethan-1,2-diol. X-ray diffraction and visual examination showed that the initial oxide form is a glassy solid and that the lattice order increases with temperature. CoFe₂O₄ and NiFe₂O₄ formed directly from the glassy state but a 2Fe∶:1Mn mixture initially forms Fe₂O₃ and an unidentified manganese oxide. These reacted at 1200° C to form MnFe₂O₄.