Investigation of the Crystal Structure and Magnetic Properties of BiMnO3+δ (δ=0.08 and 0.14) by the Methods of Neutron Diffraction and Magnetometry

The crystal structure of BiMnO3 + delta ceramic compositions is studied depending on the nominal oxygen content and temperature using neutron diffraction, X-ray diffraction and magnetometry methods. It is found that at room temperature the composition with delta = 0.08 is characterized by a monoclinic structure, while the composition with delta = 0.14 is characterized by a two-phase state with the coexistence of a dominant orthorhombic structure and a monoclinic structure. An increase in temperature leads to a structural phase transition to a nonpolar orthorhombic structure at temperatures of T-1 similar to 500 K and T-2 similar to 750 K for the compositions delta = 0.08 and delta = 0.14, respectively, while the orthorhombic structure is retained in both compositions up to the temperatures of chemical decomposition. With an increase in the nominal oxygen content from delta = 0.08 to delta = 0.14, the magnetization of the compositions decreases, which is due to destruction of the orbital ordering of Mn3+ ions, while the magnetic state of the compositions changes from ferromagnetic (delta = 0.08) with a temperature of transition to the magnetically ordered state of T-C1 approximate to 68 K to the spin-glass-type state (delta = 0.14) with the freezing temperature of magnetic clusters of T-C2 approximate to 28 K.