Ferromagnetic compounds of manganese with perovskite structure

Various manganites of the general formula La3+Mn3+O32−-Me2+Mn4+O32− have been prepared in the form of polycrystalline products. Perovskite structures were found, i.a. for all mixed crystals LaMnO3CaMnO3, for LaMnO3SrMnO3 containing up to 70% SrMnO3, and for LaMnO3BaMnO3 containing less than 50% BaMnO3. The mixed crystals with perovskite structure are ferromagnetic. Curves for the Curie temperature versus composition and saturation versus composition are given for LaMnO3CaMnO3, LaMnO3SrMnO3, and LaMnO3BaMnO3. Both types of curves show maxima between 25 and 40% Me2+Mn4+O32−; here all 3d electrons available contribute with their spins to the saturation magnetization. The ferromagnetic properties can be understood as the result of a strong positive Mn3+Mn4+ exchange interaction combined with a weak Mn3+Mn3+ interaction and a negative Mn4+Mn4+ interaction. The Mn3+Mn4+ interaction, presumably of the indirect exchange type, is thought to be the first clear example of positive exchange interaction in oxidic substances.