The micromagnetic structure and magnetization process of perpendicular Y3 Fe5 O12 (YIG) films were studied by Lorentz microscopy and electron holography. The closure domain structure inside the thin transmission electron microscopy specimen exhibits the same period as the magnetization pattern observed by magnetic force microscopy indicating the perpendicular anisotropy of the YIG film. Through observation of stray fields, it is concluded that the shapes of domain and domain walls are sensitive to the specimen thickness; moreover, a closure domain configuration observed in thin specimen is the stable energy state as determined by the balance between the crystalline anisotropy and shape anisotropy. Domain wall movement is observed by applying a magnetic field, in situ, inside the microscope in both horizontal and perpendicular directions; the saturation fields observed are qualitatively in agreement with the results of the hysteresis loop.
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