Magnetic phase transitions in the system La1-xBixMnO3+λ

The crystal structure and magnetic properties of the La1-xBixMnO3+lambda system (0less than or equal toxless than or equal to1;lambdaless than or equal to0.08) are studied as functions of the oxygen and bismuth contents. In oxidized samples La1-xBixMnO3+lambda 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 xless than or equal to0.6 and then transform into a ferromagnetic state. It is supposed that the Bi3+ ions stabilize the d(x)(2)-y(2) orbitals in the nearest Mn3+ ions whereas the d(z)(2) orbitals of the La3+ ions are stabilized. The orbitally disordered phases and d(x)(2)-y(2)-orbitally ordered phases are ferromagnetic, the d(z)(2)-orbitally ordered phases show antiferromagnetic ordering, and the state of the orbital glass type corresponds to a state of the spin glass type. (C) 2002 American Institute of Physics.