Ferromagnetic compounds of manganese with perovskite structure

Abstract Various manganites of the general formula La 3+ Mn 3+ O 3 2− -Me 2+ Mn 4+ O 3 2− have been prepared in the form of polycrystalline products. Perovskite structures were found, i.a. for all mixed crystals LaMnO 3 CaMnO 3 , for LaMnO 3 SrMnO 3 containing up to 70% SrMnO 3 , and for LaMnO 3 BaMnO 3 containing less than 50% BaMnO 3 . The mixed crystals with perovskite structure are ferromagnetic. Curves for the Curie temperature versus composition and saturation versus composition are given for LaMnO 3 CaMnO 3 , LaMnO 3 SrMnO 3 , and LaMnO 3 BaMnO 3 . Both types of curves show maxima between 25 and 40% Me 2+ Mn 4+ O 3 2− ; here all 3 d electrons available contribute with their spins to the saturation magnetization. The ferromagnetic properties can be understood as the result of a strong positive Mn 3+ Mn 4+ exchange interaction combined with a weak Mn 3+ Mn 3+ interaction and a negative Mn 4+ Mn 4+ interaction. The Mn 3+ Mn 4+ interaction, presumably of the indirect exchange type, is thought to be the first clear example of positive exchange interaction in oxidic substances.