Ab initio comparative study of the magnetic, electronic and optical properties of AB(2)O(4) (A, B= Mn, Fe) spinels

The comparison of the magnetic, electronic, and optical properties of the spinel transition-metal oxides AB(2)O(4) (A, B = Fe, Mn) and their relationship with the structure and composition were studied within DFT-GGA + U approximation. The spinels were considered both in the normal and inverse structure. We have found that regardless of composition and structure, the studied spinels are ferrimagnetic with antiparallel magnetic moments on Aand B-site cations. Electronic and structural properties of spinels depend on the composition: FeMn2O4 has a tetragonal structure and half-metallic properties; however, in the inverse FeMn2O4, the bandgap opens for the spin-up channel. MnFe2O4 is a cubic insulator with a bandgap of about 1.5 eV, which decreases in the inverse structure. The superexchange constants estimate within the simple indirect coupling model and have values close to the experimental ones. The total magnetization of FeMn2O4 is drop-down to zero under hydrostatic pressure above 60 GPa due to the strong dependence of the magnetic moment of octahedral manganese ion on the pressure. The microscopic mechanisms of the relationship between the structure, composition and properties are studied.