| Summary: | 碩士 === 國立臺灣海洋大學 === 光電科學研究所 === 97 === We have studied variation of magnetization reversal in nanometer wide single layer NiFe elliptical rings with various aspect ratios and with different inter-unit distance, using longitudinal magneto-optical Kerr effect magnetometer (L-MOKE) and micro-magnetic simulation (OOMMF). Our home-made L-MOKE is capable of measuring the hysteresis loops of 100nm wide samples. We kept the circumferences of the elliptical rings around 6.3 μm but changed the length of long axis and short axis. The magnetization reversal of NiFe elliptical rings as functions of the film thickness and aspect ratio was investigated in detail. According to our experiment, the flux-closure vortex state was found in thick films and small aspect ratios. The two-step switching behavior occurred in these elliptical rings (onion state→vortex state→onion state).
MOKE is an optical measurement system and the spot size of laser is 5~50μm. When the sample size was varied down to nanometer scale, we used arrays of elliptical rings to increase the signal-to-noise ratio. In arrays of elliptical rings, the magnetostatic interaction influenced the magnetization reversal. In the previous research, when the distance between circular rings was reduced, the magnetostatic interaction would be very strong due to the stray field. In this part of the thesis, we changed the distance by a shifted arrangement for every other rows in the short axis direction. The position was fixed in the short axis direction and the distance in the long axis direction was changed to investigate the magnetostatic interaction.
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