Influence of strain on optical properties of multiferroic EuTiO_3 film: A first-principles investigation

摘要

We use first-principles calculations based on the density functional theory to investigate the magnetic properties, optical properties, and electronic structure of perovskite-type multiferroic EuTiO_3 (ETO) thin films with biaxial strain. The calculations indicate that, in ETO films, the magnetic moment of Eu ions and the energy of the direct band gap decrease slowly (increase rapidly) with increasing compressive (tensile) strain. A direct band gap tunable from 1.0 to 1.52 eV is expected in ferroelectric and ferromagnetic ETO thin films upon application of 1%-4% tensile strain, and photogenerated carriers with spin-polarization can be induced from Eu 4f to Ti 3d states. This behavior can be confirmed by monitoring the strain-dependent optical absorption coefficient of ETO thin films and is explained by the shift of the strain-tuned electronic structure. These results suggest the potential applications of ETO thin films in multiferroic photovoltaic cells.