Manganese based spinel – like ceramics with NTC – type thermistor behaviour

The structural, electrical and magnetic properties of the spinel-type MgGa2 − xMnxO4 compounds have been studied. The samples were prepared by standard solid state reaction method and characterized by X-ray diffraction (XRD), temperature dependent resistivity ρ(T) and magnetic M(T) measurements. The XRD patterns reveal a cubic structure (Fd-3m, S.G. No. 227) for all the solid solutions, with x values ranging from 0.1 to 1, confirming the spinel-type structure and the good solubility of Mn in MgGa2O4. The material becomes less resistive as the substitution increase. However the ρ(T) remains quasi-linearly dependent, the range of sensitivity being shifted to lower temperatures. The magnetic characterization showed that with an increase in the manganese content all the samples display paramagnetic behaviour in high temperature range, magnetic ions interacting antiferromagnetically at low temperature. The values of the effective magnetic momentum (μeff) decrease down to about 4 μB, as the manganese content increases, reflecting the possible shift of the valence of manganese towards Mn4+. This last effect enables us to suppose that carrier concentration may increase by increasing manganese content and thus improving the electrical conduction through the well-known electron “hopping” mechanism, which is believed to act in this kind of materials. udy highlights the possibility of modelling these manganite-type materials for improved properties, intended to negative temperature coefficient (NTC) type thermistor, for high temperature applications.