| BiFeO3 is the only known room temperature single-phase multiferroic material. The ferroelectric order in BiFeO3 is coupled with the anti-ferromagnetic order, making this material prosing in multifunctional devices. In this work, we use pulsed laser deposition (PLD) to deposit a series of BiFeO3-based epitaxial heterostructures, and study the structure, electrical and magnetic properties. The achievements include:(1) Important deposition parameters such as substrate temperature, oxygen pressure, laser energy density and repetition rate are optimized for epitaxial deposition of BiFeO3, La0.7Sr0.3MnO3 and SrRuO3 films on SrTiO3 (001) single crystal substrates. The structure and morphology of these films are characterized with X-ray diffraction, atomic force microscopy and scanning electron microscopy.(2) BiFeO3/Lao.7Sro.3MnO3 heterostructures were deposited and characterized. By corona poling, ferroelectric polarization in BiFeO3 is switched. Exchange bias, which itself is controlled by the direction of polarization, is observed as a shift of M-H hysteresis loops. The exchange bias is a result of the interface coupling between ferromagnetic La0.7Sr0.3MnO3 and antiferromagnetic BiFeO3, which itself is coupled with ferroelectric order.(3) Resistive switching of BiFeO3 is studied by using various metal electrodes such as Pt, Lao.7Sro.3Mn03, SrRuO3 and In. In Pt/BiFeO3/La0.7Sr0.3MnO3, clear resistance switch can only be observed by a negative pulse, while it could be observed with either a positive or a negative pulse by replacing La0.7Sr0.3MnO3 with SrRuO3. No resistive switching is observed in In/BiFeO3/La0.7Sr0.3MnO3. These indicate that the resistive switching in these heterostructures are dominated by the polarization modulated Schottky barrier formed between ferroelectric BiFeO3 and the electrodes. Low work function metals La0.7Sr0.3MnO3 and In cannot form a high Schottky barrier with BiFeO3, and therefore, have little contribution to the resistive switching observed. |
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