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Local Variation of Magnetic Parameters of the Free Layer in TMR Junctions
CheolGi Kim,Toshihiro Shoyama,Masakiyo Tsunoda,Migaku Takahashi,Tae Hyo Lee,Chong-Oh Kim 한국자기학회 2002 Journal of Magnetics Vol.7 No.3
Local M-H loops have been measured on the free layer of a tunneling magnetoresistance (TMR) junction using the magneto-optical Kerr effect (MOKE) system, with an optical beam size of about 2 ㎛ diameter. Tunnel junctions were deposited using the DC magnetron sputtering method in a chamber with a base pressure of 3 × 10^(-9) Torr. The relatively irregular variations of coercive force Hc (~17.5 Oe) and unidirectional anisotropy field Hua (~7.5 Oe) in the as-deposited sample are revealed. After 200 ℃ annealing, Hc decreases to 15 Oe but Hua increases to 20 Oe with smooth local variations. Two-dimensional plots of Hc and Hua show the symmetric saddle shapes with their axes aligned with the pinned layer, irrespective of the annealing field angle. This is thought to be caused by geometric effects during deposition, together with a minor annealing effect. In addition, the variation of root mean square (RMS) surface roughness reveals it to be symmetric with respect to the center of the pinned-layer axis, with the roughness of 2.5 Å near the edge and 5.8 Å at the junction center. Comparison of surface roughness with the variation of Hua suggests that the Hua variation of the free layer is well described by dipole interactions related to surface roughness. As a whole, the reversal magnetization is not uniform over the entire junction area and the macroscopic properties are governed by the average sum of local distributions.
Al6061합금의 PEO 피막 형성에 미치는 AC 전류밀도의 영향
박철기(Cheolgi Park),문성모(Sungmo Moon),정인모(Inmo Cheong),윤대수(Daesoo Yun) 한국표면공학회 2019 한국표면공학회지 Vol.52 No.3
In this work, PEO (Plasma Electrolytic Oxidation) film formation behavior of Al6061 alloy was investigated as a function of applied current density of AC at 310 Hz in the range from 120 mA/cm² to 300 mA/cm² in 0.5 M Na₂SiO₃ solution. When applied current density is lower than a critical voltage of about 132 mA/cm², voltage reaches a steady-state values less than 120 V without generation of arcs and metallic color of the alloy surface remains. On the other hand, when applied current density exceeds about 132 mA/cm², voltage increases continuously with time and arcs are generated at more than 175 V, resulting in the formation of PEO films with grey colors. Two different types of arcs, large size and small number of arcs with orange color, and small size and large number of arcs with white color, were generated at the same time when the PEO film thickness exceeds about 50 μm, irrespective of applied current density. Formation efficiency of the PEO films was found to increase with increasing applied current density and the growth rate was obtained to be about 5 μm/min at 300 mA/cm². It was also found that surface roughness of the PEO films with 70 μm thickness is not dependent on the applied current density.
김철기(CheolGi Kim) 한국자기학회 2010 韓國磁氣學會誌 Vol.20 No.4
To meet on going challenges in nano-biomedical technology, the convergence of “spintronics”, “biomedical” technology is a major break through in imaging, diagnosis and therapy, high-throughput genomic analysis. Especially magnetic bioassay is one of crucial devices for early diagnosis of specific analytes, point-of-care and U-health care application. In this paper, current status on high resolution magnetic sensors for bioassay and on-chip magnets for biomolecule transportation will be reviewed.
이철기 ( Lee Cheolgi ) 한국문법교육학회 2020 문법 교육 Vol.40 No.-
Over the past few years, a considerable number of studies have been made on inquiry-based language learning. These studies lay the groundwork for inquiry-based language learning can be understood as a cognitive process of thinking. Some studies named this cognitive process as Grammatical thinking. The purpose of this study was to demonstrate that Grammatical thinking is scientific thinking and scientific reasoning. I have revealed that the existing five-step of the inquiry-based learning process is based on Karl Popper's the hypothetico-deductive method. And I have revealed that Karl Popper's the hypothetico-deductive method is based on Charles Sanders Peirce's philosophy of science. Besides, the hypothetico-deductive method can be applied to inquiry-based language learning as well as inquiry in science and social studies. This study is intended to contribute to theoretically explain the e ssence of inquiry-based language learning. Based on this study, I look forward to designing inquiry tasks or activities about gramma r that can improve learners' ability to think grammatically.