| Summary: | 碩士 === 國立清華大學 === 物理系 === 101 === Magnetoelectric coupling in multiferroic materials has attracted much attention because the exciting application potential in multiply controlled devices. Among the few room-temperature single-phase magnetoelectric multiferroics reported, BiFeO3 shows the strong coupling between antiferromagnetic and ferroelectric types of order. Hence these multiferroic matericals are of interest for memory and logic device applications. First, the (001)-oriented BiFeO3 thin film is synthesized by the pulsed laser deposition technique (PLD). We unravel the charge, orbital, and the antiferromagnetic properties of BiFeO3 films using soft X-ray absorption spectroscopy (XAS) based on X-ray linear dichroism (LD) and magnetic X-ray linear dichroism (MLD). Simultaneously we have been pursuing approaches to understand the origin of the magnetic properties using X-ray magnetic circular dichroism (XMCD) and SQUID measurements. And hard x-ray photoemission spectroscopy (HXPES) is a powerful method can direct unravel the electronic structure. The HXPES results show the peak of Fe-2p3/2 was separated at the BiFeO3 thin films. We explain these double peaks are closely related to the multiplet structure of Fe3+. The difference in energy between the peaks was 1.15 eV. In addition, the comparison between data from the normal BFO and BFO which was cooled under a reduced O pressure (90 m torr) indicates that the HXPES data is no different. We also spent a lot of effort to measure HAXPES of BFO grown on different substrates as planned. It is clear that the HAXPES data of BFO grown differ much; we are doing calculations to extract physics out of these data. The preliminary results are quite encouraging.
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