| Summary: | 碩士 === 國立彰化師範大學 === 物理學系 === 92 === The objective of this study is to investigate the size effects on the switching fields of microstructured permalloy rings. A series of ring-shaped permalloy (Ni80Fe20) elements with diameters of 2 to 5 mm and thicknesses of 14 to 66 nm were fabricated using electron beam lithography through a lift-off process. The characterization of magnetization reversal process was carried out by measuring the magnetoresistance with the external magnetic field applied in the film plane at room temperature. The control parameters were set to include the diameter, linewidth, and thickness of the permalloy rings.
For the dynamic behavior of magnetization configuration in the ring elements stable vortex and onion configurations and other meta-stable mixed configurations were identified. The switching fields of the vortex-to-onion transition and onion-vortex transition, i.e. Hvo and Hov respectively, were strongly size and thickness dependant. The switching fields of Hvo and Hov increase with decreasing size, which is dominated by shape anisotropy. Furthermore, Hvo increases with increasing thickness roughly, whereas Hov stayed thickness independent.
In addition, the control of magnetization configuration was also investigated by arranging a current lead running through the center of the ring, generating circulating field from the center post and Oersted field from the leads through the top/bottom of the ring on the opposite sides. These fields make no effect on Hvo but have great influence on Hov, which is due to the effective force exerted by these fields on the walls of onion state.
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