| Summary: | 碩士 === 國立清華大學 === 物理系 === 102 === BiFeO3 is a multiferroic material in which the antiferromagnetism and ferroelectricity simultaneously occur and possess the magnetoelectric coupling. Many experimental results indicate that the electronic and magnetic properties of BiFeO3 thin films can be controlled by strain engineering. The purpose of this work is to investigate the strain effects of BiFeO3 thin films grown on different substrates with varied lattice constants. The comparison between the electronic states of compressive-strained BiFeO3/LaAlO3, tensile-strained BiFeO3/NdScO3 and nearly strain-free BiFeO3/DyScO3 is particularly emphasized.
We used X-ray absorption spectroscopy (XAS) at Fe L-edge and O K-edge to explore crystal field symmetry as well as orientation of antiferromagnetic spin axis. Linear dichroism (LD) is also presented to obtain their orbital and magnetic anisotropy. The measurements suggest that Fe 3d electronic states change when BiFeO3 thin film experiences different strains. In addition, we used resonant inelastic X-ray scattering (RIXS) to further explore the electronic structure of BiFeO3 thin films. BiFeO3/SrTiO3 is chosen as the test case to measure RIXS. Since the valence of Fe is only 3+, the d-d excitations exhibit clear features which can be explained by multiplet calculations. Finally, simulated XAS and RIXS spectrum were obtained by softwares based on charge transfer multiplet scheme such as CTM4XAS and Missing. The calculated results can qualitatively reproduce the experimental features.
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