| Summary: | 碩士 === 國立交通大學 === 電子物理系所 === 102 === BFO-CFO vertically align nanocomposite (VAN) was successfully made by utilizing the different wetting conditions from BFO and CFO film when growing on STO substrate at the same time in the PLD system. From the XRD result, there was strain effect from STO substrate to BFO and CFO film. Especially for BFO-CFO/STO VAN, CFO pillar relaxed the strain of BFO film, and shifted magnetic phase transitions on BFO/STO thin film to around 30 K and 160 K as compared to that of BFO powders where the transitions occured around 55 K and 200 K, respectively. From M-T and C-T measurements on BFO/CFO/STO bilayer and BFO-CFO/STO VAN, antiferromagnetic-ferromagnetic coupling (BFO-CFO) is stronger than antiferromagnetic-ferroelectric coupling (BFO). making the magnetization and capacitance anomalies unobservable in those systems. Furthermore, the C-T beharviors of BFO/STO and BFO/CFO/STO are in general similar, but different in subtle details, which presumably originates from the quenching of spin reorientation in BFO due to ferromagnetic coupling from CFO. The situation is even more complicated in the CFO pillar embedded in BFO matrix sample. Finally, from R-T measurement, the high-density BFO-CFO/STO VAN film showed an apparent insulator-metal transition around 30 K, which is similar to that observed in BFO film under strong external magnetic fields which done by another reseach before. The result suggests that when the pillar density is large enough it may generate strong enough local magnetic field to modify the ferroelectric domain structures in BFO matrix. Further investigations are certainly in order to delineate the interisting emergent phenomena observed in the present study.
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