The investigations of magnetization reversal and magnetoresistance on patterned permalloy ring elements

• Main Authors: Lu-Kuei Lin, 林呂圭
• Other Authors: J. C. Wu
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/13042784254650152747

碩士 === 國立彰化師範大學 === 物理學系 === 93 === The magnetization configurations of microstructured permalloy (Ni80Fe20) rings and their reversal processes have been studied through magnetoresistance (MR) measurements, magnetic force microscopy (MFM), and micro-magnetism simulations, respectively. A series of ring-shaped permalloy elements were fabricated using electron beam lithography in conjunction with lift-off process. The MR measurements were carried out with low-field dc sensing current under the external magnetic field applied parallel or perpendicular to the current direction at room temperature. Consequently, the switching fields of the vortex-to-onion (HVO) and onion-to-vortex (HOV) transitions were strongly linewidth and thickness dependent: the HVO and HOV increase with decreasing linewidth, which is believed to be dominated by shape anisotropy; and the HVO increases with increasing thickness, whereas the HOV is independent of the film thickness. In addition, it was found that the size of the current/voltage leads patched on the ring plays an important role on the MR curves, as the patched areas are larger or comparable to the domain walls a short-circuiting occurs. The short-circuiting effect forms significant drops near the transition points on the longitudinal MR curves. In this issue, we designed leads with smaller radial angle which is useful to limit the short-circuiting effect. In the section of MFM imaging, a series of magnetization configurations and their reversal processes have been observed, especially the vortex-pair state and vortexcore state. In the section of micro-magnetism simulations, the opposite helicity of vortex domain wall was recognized and dominated an unusual magnetization reversal process which is without vortex state. The unusual behavior was reconfirmed in the corresponding MR curves. The micro-magnetism simulations give a good agreement with our MFM images and MR curves.