Electronic Structure of Bismuth Ferromanganite BiFe0.5Mn0.5O3

Multiferroics based on complex oxides of transition metals, particularly ferromanganite BiFe0.5Mn0.5O3, are promising functional materials for use in various electrical devices. However, in scientific publications there is no information about systematic studies of the BiFe0.5Mn0.5O3 solid solution. In this work, a model structure of rhombohedral BiFe0.5Mn0.5O3 is studied using ab initio methods. Theoretical estimations of the effective magnetic moments of iron and manganese ions, the degree of localization of the 3d states of these ions, and the energy gap for different spin configurations of Fe and Mn ions are carried out. The nature of the exchange interactions between the transition-metal ions is clarified. It is established that in the antiferromagnetic ordering, the magnetic moments of the iron and manganese ions are very close and have values of 4.16 and 4.23 μB, respectively; moreover, the 3d states of the Fe ions are localized, while the 3d states of the Mn ions, on the contrary, are delocalized and asymmetric. The presence of a small resulting magnetic moment of 0.012 μB per unit cell is shown. The nonequivalence of the positions of the Fe and Mn ions leading to the formation of an energy gap of 1.28 and 1.48 eV for spin-down and spin-up channels, respectively, is substantiated. The results obtained for the model structure make it possible to qualitatively describe the electronic structure of orthorhombic BiFe0.5Mn0.5O3 using a fourfold reduced number of ions as compared to its real structure, and significantly broaden the scope of information obtained by experimental methods on the structure and physical properties of BiFeO3–BiMnO3 solid solutions.