| Summary: | 博士 === 國立清華大學 === 材料科學工程學系 === 104 === Nanostructures features variety of structures composed by two or more materials. High interface-to volume ratio raises the impact of interface to the properties of the nanostructures. The introduction of epitaxy to the nanostructures confines the direction of interfaces and crystallographic direction, bringing an insight to the interface phenomena. In this thesis, the author discusses the magnetism in different types of epitaxial nanostructures and their correlation to the structures. Interfacial coupling and its contribution to the magnetic anisotropy are especially addressed. Three problems of magnetism of epitaxial nanostructures are involved in this thesis: the anisotropy of magnetic moment in 109° domain walls (DWs) of multiferroic bismuth ferrite (BiFeO3), magnetic anisotropy and exchange coupling in epitaxial core-shell nanostructures and how they are affected by structure geometry, growth and control of magnetic anisotropy in the epitaxial metal-oxide nanostructures. The author applies comprehensive structural and magnetic analyses as well as the macro-spin/ micromagnetic modeling and deduces the following conclusions: 1. The average direction antiferromagnetic spin in 109°DWs is parallel to the DWs with a certain out-of-plane component. No obvious anisotropy is observed of pinned uncompensated spins. 2. With micromagnetic simulation and variation of structure geometry, the author deduce that the structure geometry not only determine the magnetic anisotropy but also effect the exchange coupling in epitaxial core-shell nanostructures. 3. The metal-oxide columnar nanostructures could be fabricated by physical deposition via oxygen vacancy and difference of the oxygen affinity. Growth temperature and substrate control the dimension and orientation of nano-columns and thus the magnetic anisotropy. These results confirm that the introduction of epitaxy allow further investigation and control of interface phenomena and their anisotropy in nanostructures. The methods proposed in this thesis also helps researches of magnetic nanostructures.
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