Electric and Magnetic Properties of Multiferroic BiFeO and YMnO Thin Films

We grew rhombohedrally distorted BiFeO ₃ and hexagonal YMnO ₃ thin films on Pt/TiO ₂/SiO ₂/Si substrates via RF magnetron sputtering technique in a pure oxygen atmosphere. BiFeO ₃ and YMnO ₃ targets were self-made by the usual solid-state reaction method. We investigated the effects of deposition temperature upon crystalline structure, surface morphology, magnetization, and electrical polarization of BiFeO₃ and YMnO₃ thin films. The crystalline structure was studied by X-ray diffraction, and the topography of film surface was analyzed by atomic force microscopy. We also conducted measurements of ferroelectric and ferromagnetic hysteresis loops to study the electrical and magnetic behavior of the samples. Polarization, as a function of electric field in capacitor structures based on our BiFeO₃ films, shows hysteretic behavior with a coercive field of 54 kV/cm and a remanent polarization of 21 muC/cm²; whereas, YMnO₃ films show hysteretic behavior with coercive field of 2.4 kV/cm, remanent polarization of 1.2 muC/cm², and saturation polarization of 3.5 mu C/cm² . Magnetization measurements of the BiFeO ₃ films evidence weak ferromagnetism, that can be related to the presence of a small quantity of ferromagnetic impurities.