| Summary: | 碩士 === 國立東華大學 === 材料科學與工程學系 === 90 === Advances in lithography and pattern transfer techniques have provided the opportunity of exploring novel magnetic phenomena in controlled shapes. In particular, the magnetic thin films have been extensively investigated because of their importance in both magnetoresistance (MR) devices and more recently, magneto electronic devices. An understanding of the magnetization reversal processes and magnetoresistance (MR) response in small ferromagnetic elements is also important for the design and optimization of miniature MR heads for ultrahigh density data storage applications. There have been numerous efforts to investigate the magnetization reversal and MR behavior in Permalloy (Ni80Fe20) wires so far. Recent studies have demonstrated that the strong dependence of switching field and magnetization reversal the shape is attributed to the formation of domains, even in submicron structures, which are crucial in the magnetization reversal process.
The shape of a wire structure has a decisive influence on magnetic properties in the micron size range. For example, the MR behaviors are found to change significantly in submicron-sized Ni80Fe20 modulated octagon in arrangement of chain.
In this thesis, we have presented an arrangement in octagon Permalloy in chain, leading to a striking variation in the magnetoresistance. We’ve demonstrated that it’s possible to control the switching field by introducing the different number of rectangular Permalloy octagons in chain and facilitating magnetoresistance behavior during magnetic reversal. Our results suggested to “introducing” domain walls in patterned magnetic wire, and which can be used for studies of domain wall effect. We discussed the geometrical effect of the arrangement of the octagon chains on the switching field associated with domain configurations inferred from the magnetic force microscopy (MFM) imaging and physical property measurement system (PPMS).
After systematic experiments, we can propose that the different arrangement of octagons provides a way to control the switching field and MR Ratio of submicron permalloy wire. Of course, having suggestion that thickness and aspect ratio also have influences on the patterned permalloy wire itself during magnetization process. Based on our observation on magnetic force microscopy images, we would claim that we understand the domain characteristic during magnetization process. At remanent state, by our design of inducing magnetic unit in a wire, there will be vortex state domain take shape in the unit vertical to the chain; the domains in the units which connect to each other parallel to the chain will form a single domain aligned in the same direction. Real time magnetic force microcopy images give evidence for the results of the experiments showing that under transverse applied field that spin rotates in the unit parallel to the chain; domain change forms from vortex at remanent state to single domain aligned to the applied field. Under longitude applied field, in the unit vertical to the chain, domain change forms from vortex at remanent state to single domain vertical to the major axis aligned to the applied field. We also find that although the octagon arrangements influence the switching field, the AMR of each pattern is similar.
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