Dependence of ferroelectric and magnetic properties on measuring temperatures for polycrystalline BiFeO3 films

A multiferroic BiFeO₃ film was fabricated on a Pt/Ti/SiO₂/Si(100) substrate by a chemical solution deposition (CSD) method, and this was followed by postdeposition annealing at 923 K for 10 min in air. X-ray diffraction analysis indicated the formation of the polycrystalline single phase of the BiFeO₃ film. A high remanent polarization of 89 muC/cm² was observed at 90 K together with a relatively low electric coercive field of 0.32 MV/cm, although the ferroelectric hysteresis loops could not be observed at room temperature due to a high leakage current density. The temperature dependence of the ferroelectric hysteresis loops indicated that these hysteresis loops lose their shape above 165 K, and the nominal remanent polarization drastically increased due to the leakage current. Magnetic measurements indicated that the saturation magnetization was less than 1 emu/cm³ at room temperature and increased to approximately 2 emu/cm³ at 100 K, although the spontaneous magnetization could not appear. The magnetization curves of polycrystalline BiFeO₃ film were nonlinear at both temperatures, which is different with BiFeO₃ single crystal.