Structural, magnetic, and optical properties of BiFeO₃ and Bi₂FeMnO₆ epitaxial thin films: An experimental and first-principles study

BiFeO₃ and Bi₂FeMnO₆ films were epitaxially grown on SrTiO₃ (001) substrates by pulsed-laser deposition, and their structural, magnetic, magneto-optical and optical properties were measured. In Bi₂FeMnO₆, Fe is mainly present in the 3+ valence state, while Mn shows multivalence states. Bi₂FeMnO₆ exhibits low magnetization at room temperature and at 5 K indicating there is no significant B-site ordering. The BiFeO₃ film shows high optical transparency, while Bi₂FeMnO₆ shows high absorption loss in the infrared. Density-functional theory modeling of BiFeO₃, BiMnO₃ and Bi₂FeMnO₆ was carried out by applying the generalized gradient approximation (GGA) and GGA + U methods. The formation enthalpy of ordered Bi₂FeMnO₆ is positive for several crystal symmetries and for ferromagnetic (FM) or antiferromagnetic (AFM) spin structures at 0 K temperature, indicating _B-site ordering is not favored. The electronic structure calculations are consistent with the electronic and optical properties of these films.