Magnetic phase transitions in the system La1-xBixMnO3+l

Дефекты в кристаллах

Анотація

The crystal structure and magnetic properties of the La_1-xBi_xMnO_3+l system( ; 0 £ x1£ l £ 0.08 ) are studied as functions of the oxygen and bismuth contents. In oxidized samples La_1-xBi_xMnO_3+l 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 La_1-xBi_xMnO₃ are weak ferromagnets down to x £ 0.6 and then transform into a ferromagnetic state. It is supposed that the Bi³⁺ ions stabilize the d_x²-y² orbitals in the nearest Mn³⁺ ions whereas the d_z² orbitals of the La³⁺ ions are stabilized. The orbitally disordered phases and d_x²-y² - orbitally ordered phases are ferromagnetic, the d_z² - orbitally ordered phases show antiferromagnetic ordering, and the state of the orbital glass type corresponds to a state of the spin glass type.