| Summary: | 碩士 === 國立交通大學 === 電子物理系所 === 107 === The spin-state transition of perovskite LaCoO3 is an interest and important subject, which has received much attention for decades. Recently theoretical research predicts a strained LaCoO3 thin film could be a good candidate of an excitonic insulator. We have grown epitaxial LaCoO3 thin films on LSAT substrates of various orientations and also performed magnetization measurements on these films. For both zero-field cooling (ZFC) and field cooling (FC) processes, the magnetization measurements of LaCoO3 / LSAT(001) show a sharp increase of magnetic moment at 80 K. These measurements indicate that its saturated magnetic moment is higher than 0.4 μB/Co, suggesting LaCoO3 thin films that are predominantly of high-spin states (HS) at low temperature . The X-ray absorption (XAS) lineshape of LaCoO3 thin films are slightly different from that of bulk LaCoO3 at 30 K, because of the existence of HS states in LaCoO3 thin films. Resonant inelastic X-ray scattering (RIXS) is a powerful method to study electronic structure of quantum materials. Our RIXS results reveal HS states in LaCoO3 thin films of 90 nm and 20 nm at 20 K, like the HS states of bulk LaCoO3 at the room temperature. In summary, tensile strain is a critical factor for stabilizing the spin state, and a strained LaCoO3 thin film is a good candidate for realizing an excitonic insulator.
|
|---|
