Influence of Mn2+ in the magnetic behaviour of manganese related-perovskites

Two series of oxygen deficient perovskites with composition La0.5Ca0.5MnO3-delta have been prepared by different synthetic routes. Magnetic measurements indicate that samples with same degree of anionic vacancies (identical 6 value) have different behavior. A systematic study of a large set of samples shows that depending on the synthesis protocol followed to induce the anionic vacancies different species of manganese can be stabilized. To confirm this assumption, a detailed XANES study has been carried out together with X-ray diffraction, electron diffraction and thermogravimetric analysis, for a large set of samples. Our results indicate the coexistence of Mn2+, Mn3+ and Mn4+ species for those samples obtained from a La0.5Ca0.5MnO2.5 parent compound. However, only Mn3+ and Mn4+ species are stabilized when the synthesis is based on direct reduction of La0.5Ca0.5MnO3. Reduction and oxidation mechanism and magnetic properties are discussed as a function of the Mn oxidation states. (c) 2006 Elsevier Ltd. All rights reserved.