Magnetic susceptibility study on Li-Mn spinel oxides

Li-Mn spinel oxide particles were prepared by the solid state reaction using Mn3O4 particles and Li-hydroxide monohydrate, and the effects of the reaction temperature on the produced phase were studied with the powder X-ray diffraction and the magnetic susceptibility measurement. From the lattice constant variation versus the reaction temperature, it was found that the spinel oxides prepared by low temperature reaction were cation deficient type, and that the cation deficient degree decreased with an increase in the reaction temperature. The asymptotic Curie temperature (Weiss constant), derived from the temperature dependent magnetic susceptibility, was always negative, and it implied that the antiferromagnetic coupling among Mn ions is dominant. The absolute value of the Weiss constant increased with the reaction temperature, took a maximum at the reaction temperature around 750°C, and then decreased with a further increase in the reaction temperature. These were attributed to the variation of the average valence of Mn ions. At the reaction temperature, where the absolute value of the Weiss constant takes a maximum, the non-stoichiometry of Li-Mn spinel oxide becomes minimum. In the specimen prepared above the temperature, it was likely that there existed oxygen vacancy, and the phase transformation between cubic and orthorhombic structures was found in the DSC curves.