• Proceedings of the Korean Magnestics Society Conference
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• 2012.11a
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• pp.59-60
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• 2012

• Proceedings of the Korean Magnestics Society Conference
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• 2004.06a
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• pp.202-203
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• 2004

• Proceedings of the Korean Magnestics Society Conference
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• 2013.12a
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• pp.108-109
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• 2013

• Proceedings of the Korean Magnestics Society Conference
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• 2008.12a
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• pp.68.2-68.2
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• 2008

• Journal of the Korean Magnetics Society
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• v.10 no.5
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• pp.232-236
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• 2000

CoSm thin films with a Cr underlayer have received continuous attention as a potential material for a high density longitudinal magnetic recording media. In this study the Ax gas sputtering pressure effects on the magnetic properties of CoSm thin films, which were fabricated by using a dc magnetron sputtering machine, were investigated. The magnetic switching volume is especially important parameter to understand the thermal stability of the written information, magnetization reversal process and media noise. Therefore, in this paper the effects of sputtering pressure on the magnetic switching volume of CoSm thin films grown on Cr underlayer with the same sputtering conditions was studied. As the Ar sputtering pressure during sputtering of the CoSm magnetic layer increases from 5 to 30 mTorr, the measured switching volumes decreased from 9.0 to 5.2$\times$10$^{-18}$ cm$^3$. The calculated diameter of switching unit from V＊ was less than 22 nm, which satisfies the Sharrock's requirement on the thermal stability of the high density longitudinal magnetic recording media.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.67.1-67.1
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• 2016

We examined the relations between CME speed and properties of magnetic helicity in the source region such as helicity injection rate and total unsigned magnetic flux, which reflect the magnetic energy in the active region. For this, we selected 22 CMEs occurred during the increasing phase of solar cycle 24, which shows extremely low activities and classified them into two groups according to evolution pattern of helicity injection rate. We then compared the relations with those from previous study based on the events in solar cycle 23. As the results, we found several properties as follows: (1) Both of CME speed and helicity parameters have very small values since we only considered increasing phase; (2) among 22 CMEs, only 6 events (27%) are classified as group B, which show sign reversal of helicity injection and they follow behind of appearance of group A events. This fact is well coincide with the trend of solar cycle 23 that only group A events was observed in the first 3 years of the period; (3) as the solar activity is increasing, the CME speed and helicity parameters are also increasing. Based on the observations of solar cycle 23, the helicity parameters was still increasing in spite of decreasing solar activity after maximum period.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.06a
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• pp.272-273
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• 2003

Spin dynamics has been investigated intensively in various kinds of fields. Most popular one is an initial permeability at high frequency. Also, magnetic after-effect such as thermal fluctuation of fine magnetic particles and disaccommodation in soft magnetic materials were extensively studied in the past. When we apply an external farce with the same frequency as that of the system being examined, the system absorbs the external energy and the precession enhances. It is called resonance in general. Among the various resonances, ferromagnetic resonance (FMR) has been used as a good tool to evaluate material constants such as saturation manetization or spin damping parameter by analyzing a resonance curve. In this talk first instinctive understanding of Gilbert spin damping and spin pumping will be explained. Then, experimental data for enhancement of Gilbert damping parameter (G) evaluated from FMR spectrum and spin precession measured by a time resolved pump-probe method for Permalloy thin film will be introduced. Finally, magnetization reversal observed by air-coplanar probe will be given.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.366-366
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• 2010

Single crystalline Fe/NiO bilayers were epitaxially grown on Ag(001) and on MgO(001), and investigated by Low Energy Electron Diffraction (LEED), Magneto-Optic Kerr Effect (MOKE), and X-ray Magnetic Linear Dichorism (XMLD). We find that while the Fe film has an in-plane magnetization in both Fe/NiO/Ag(001) and Fe/NiO/MgO(001) systems, the NiO spins switch from out-of-plane direction in Fe/NiO/MgO(001) to in-plane direction in Fe/NiO/Ag(001). These two different NiO spin orientations generate remarkable different effects that the NiO induced magnetic anisotropy in the Fe film is much greater in Fe/NiO/Ag(001) than in Fe/NiO/MgO(001). XMLD measurement shows that the much greater magnetic anisotropy in Fe/NiO/Ag(001) is due to a 90o-coupling between the in-plane NiO spins and the in-plane Fe spins which causes a switching of the NiO spins during the Fe magnetization reversal.

• Proceedings of the Korean Magnestics Society Conference
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• 2007.05a
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• pp.99.2-99.2
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• 2007

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.50.2-50.2
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• 2010

Magnetic helicity injection in 28 solar active regions producing 46 CMEs was investigated to find its relationship with the occurrence and speed of CMEs. The helicity injection in the active regions under investigation was calculated using full-disk 96 minute MDI magnetograms. The major findings of this study are as follows. First, the 46 CMEs are categorized into two different groups by two characteristic evolution patterns of helicity injection in their active regions: (1) a monotonically increasing of helicity accumulation (Group A; 30 CMEs in 23 active regions) and (2) significant helicity injection followed by its sign reversal (Group B; 16 CMEs in 5 active regions). Second, a fairly good correlation between the helicity injection rate and the CME speed is found for the 30 CME events in Group A. Further statistical studies, however, are needed to check whether the two characteristic helicity patterns are shown in other CME-productive active regions.