Structural, magnetic, and optical properties of BiFeO3 and Bi2 FeMnO6 epitaxial thin films: An experimental and first-principles study

BiFeO3 and Bi2 FeMnO6 films were epitaxially grown on SrTiO3 (001) substrates by pulsed-laser deposition, and their structural, magnetic, magneto-optical and optical properties were measured. In Bi2 FeMnO6, Fe is mainly present in the 3+ valence state, while Mn shows multivalence states. Bi2 FeMnO6 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 Bi2 FeMnO6 shows high absorption loss in the infrared. Density-functional theory modeling of BiFeO3, BiMnO3 and Bi2 FeMnO6 was carried out by applying the generalized gradient approximation (GGA) and GGA+U methods. The formation enthalpy of ordered Bi2 FeMnO6 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.