スピン エレクトロニクス オウヨウ ニ ムケタ キョウジセイ サンカブツ ハンドウタイ ノ カイハツ

京都大学0048新制・課程博士博士(工学)甲第13829号工博第2933号新制||工||1433(附属図書館)UT51-2008-C745京都大学大学院工学研究科材料化学専攻(主査)教授 平尾 一之, 教授 横尾 俊信, 教授 田中 勝久学位規則第4条第1項該当Doctor of EngineeringKyoto UniversityDA

Magnetic properties of ilmenite-hematite solid-solution thin films: Direct observation of antiphase boundaries and their correlation with magnetism

To clarify the relationship between nanostructures and magnetic properties of FeTiO3-Fe2O3 solid-solution thin films, we have carried out dark-field transmission electron microscope (DF-TEM) and high-angle annular dark-field (HAADF) scanning transmission electron microscope (STEM) observations. The ordered-phase films show strong ferrimagnetic properties while the films identified as the disordered phase according to x-ray diffraction are weakly ferrimagnetic with high saturation fields, in contrast to completely disordered FeTiO3-Fe2O3 solid solution for which antiferromagnetic properties or rather small magnetizations are expected. The DF-TEM and HAADF-STEM observations revealed that the ordered-phase films typically consist of cation-ordered domains of over 200 nm and that the Fe and Fe-Ti layers stacked alternately along the c axis, which leads to strong ferrimagnetic properties, are clearly distinguishable from each other. On the other hand, the films identified as the disordered phase are found to possess short-range ordered structure with antiphase boundaries distributed in cation-disordered matrix, rather than completely random cation distribution, explaining why the films are weakly ferrimagnetic with high saturation fields. The results demonstrate the significance of atomic-level observation of the cation distribution in this system for understanding the magnetic properties

Reduction Mechanism for CeO2 Revealed by Direct Observation of the Oxygen Vacancy Distribution in Shape‐Controlled CeO2

Abstract CeO2 and CeO2‐based materials are widely used as catalysts and catalyst supports for a variety of chemical reactions. The ability to form oxygen vacancies plays an important role in the catalytic activities in these materials. Therefore, revealing the reduction mechanism for CeO2 is crucial to understanding the catalytic activities. In this study, shape‐controlled CeO2 nanoparticles are fabricated and the distribution of surface oxygen vacancies on the (100) and (111) surfaces is systematically studied using scanning transmission electron microscopy and electron energy‐loss spectroscopy and the response to H2 reduction treatment. It is successfully demonstrated that both catalytic activities and the ability to form oxygen vacancies are strongly dependent on the type of lattice planes. Moreover, the present results provide important insights into the reduction mechanism for CeO2, in which bulk oxygen instead of the widely believed surface capping oxygen makes no small contribution to the initial reduction step