Ferroelectric and magnetic properties of multiferroic BiFeO3-based composite films

BiFeO₃-based composite films were fabricated onto the Pt/Ti/SiO₂/Si(100) substrates by a chemical solution deposition (CSD) method using the precursor solutions with various excess iron composition followed by annealing at 923 K for 30 minutes under oxygen gas flow. Coexistence of spontaneous magnetization and remanent polarization could be obtained in the BiFeO₂-based composite films with high excess iron composition. The remanent magnetization of almost 20 emu/cm³ and the magnetic coercive field of 1.5 kOe were obtained at the iron composition ratio of Fe/Bi = 1.25. In this specimen, the remanent polarization at 90 K was approximately 10 muC/cm² at the electric field of 1500 kV/cm. Structural analysis suggested that the remanent polarization has a possibility to increase by suppressing the formation of the secondary phases of Bi₂Fe₄O₉ and alpha-Fe₂O₃, these are the nonferroelectric material as well as antiferromagnetic phase.