Magnetic Study of the Manganate Phases: CaMnO3, Ca4Mn3O10, Ca3Mn2O7, Ca2MnO4

Abstract

Two series of manganate phases have been prepared and their magnetic properties measured. The first series consists, in addition to CaMn${\mathrm{O}}_3$, of three phases having layered structures. In these, tetravalent magnanese ions are contained in single or multiple perovskite layers which are separated from each other by nonmagnetic calcium-oxygen layers. Magnetic exchange of the type ${\mathrm{Mn}}^{4+}$-O-${\mathrm{Mn}}^{4+}$ is disrupted between layers, and decreased Néel temperatures were expected to result. In a second series of phases, the size of of the CaMn${\mathrm{O}}_3$ unit cell was increased by partial substitution of strontium for calcium. Increased separation of manganese ions produced by this means was expected to reduce Néel temperatures. However, contrary to these expectations, Néel temperatures remained approximately constant for the first series of phases and increased for the second.