Magnetic phase transitions in the system La₁₋xBixMnO₃₊λ

Abstract

The crystal structure and magnetic properties of the La₁₋xBixMnO₃₊λ system (0⩽x⩽1;λ⩽0.08) are studied as functions of the oxygen and bismuth contents. In oxidized samples La₁₋xBixMnO₃₊λ a phase transition from a ferromagnetic state (rhombohedric phase) to a state of the spin glass type (quasitetragonal phase) is observed with increase of the bismuth concentration. The reduced samples La₁₋xBixMnO₃ are weak ferromagnets down to x⩽0.6 and then transform into a ferromagnetic state. It is supposed that the Bi³⁺ ions stabilize the dx2−y2 orbitals in the nearest Mn³⁺ ions whereas the dz2 orbitals of the La³⁺ ions are stabilized. The orbitally disordered phases and dx2−y2-orbitally ordered phases are ferromagnetic, the dz2-orbitally ordered phases show antiferromagnetic ordering, and the state of the orbital glass type corresponds to a state of the spin glass type.

The crystal structure and magnetic properties of the La₁₋xBixMnO₃₊λ system (0⩽x⩽1;λ⩽0.08) are studied as functions of the oxygen and bismuth contents. In oxidized samples La₁₋xBixMnO₃₊λ a phase transition from a ferromagnetic state (rhombohedric phase) to a state of the spin glass type (quasitetragonal phase) is observed with increase of the bismuth concentration. The reduced samples La₁₋xBixMnO₃ are weak ferromagnets down to x⩽0.6 and then transform into a ferromagnetic state. It is supposed that the Bi³⁺ ions stabilize the dx2−y2 orbitals in the nearest Mn³⁺ ions whereas the dz2 orbitals of the La³⁺ ions are stabilized. The orbitally disordered phases and dx2−y2-orbitally ordered phases are ferromagnetic, the dz2-orbitally ordered phases show antiferromagnetic ordering, and the state of the orbital glass type corresponds to a state of the spin glass type.