• Proceedings of the Korean Magnestics Society Conference
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• 2004.12a
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• pp.89-90
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• 2004

• Korean Journal of Materials Research
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• v.4 no.5
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• pp.535-540
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• 1994

Thin film magnet was fabricated by radio frequency magnetron sputtering using $Nd_13/(Fe.Co)_{70}B_{17}$ alloy target and magnetic properties were investigated according to sputtering conditions from the metallurgical point of view. we could obtain the best preferred orientation of $Nd_2Fe_{14}B$ phase at substrate temperatures between $450^{\circ}C$ and $460^{\circ}C$ with the input power 150W, and thin films had the anisotropic magnetic properties. But, as the thickness of thin film increased, the c-axis orientation gradually tended to be disordered and magnetic properties also become isotropic. Just like Nd-Fe-B meltspun ribbon, the microstructure of thin film magnet was consisted of very find cell shaped $Nd_2Fe_{14}B$ phase and the second phase along grain boundary. While, domain structure showed maze patterns whose magnetic easy axis was was perpendicular to film plane of thin film. It was concluded from these results that the perpendicualr anisotropy in magnetization was attributed to the perpendicular alignment of very find $Nd_2Fe_{14}B$ grains in thin film.

• Journal of the Korean Magnetics Society
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• v.1 no.2
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• pp.31-36
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• 1991

Structural and compositional heterogeneities of sputter deposited, amorphous $Co_{87}Zr_{4}NB_{9}$ thin films were investigated using TEM and EDS with windowless detector. The films deposited with substrate bias and annealed in rotating magnetc field showed two amorphous phases of Co-rich region and (ZrNb)oxide-rich region, and revealed 'ultra-soft' magnetic properties. Revesible bias-responses and overdamped frequency responses, along with small Hc, Hk and Mr/Ms ratio, give the possibility of ultra-soft magnetic behavior fo CoZrNb thin films. We proposed the vortex type magnetization distribution in remanent state which was correlated with the thin film heterogeneity. Then, the ultra-soft characteristics of the compositionally heterogeneous films were explained by the spin vortices that minimized the total magnetostatic and exchange coupling energies.

• Journal of Magnetics
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• v.21 no.2
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• pp.159-163
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• 2016

Antiferromagnet (AFM)/ferromagnet (FM) bilayer structures are widely used in the magnetic devices of sensor and memory applications, as AFM materials can induce unidirectional anisotropy of the FM material via exchange coupling. The strength of the exchange coupling is known to be sensitive to quality of the interface of the AFM/FM bilayers. In this study, we utilize proton irradiation to modify the interface structures and investigate its effect on the magnetic properties of AFM/FM structures, including the exchange bias and magnetic thermoelectric effect. The magnetic properties of IrMn/CoFeB structures with various IrMn thicknesses are characterized after they are exposed to a proton beam of 3 MeV and $1{\sim}5{\times}10^{14}ions/cm^2$. We observe that the magnetic moment is gradually reduced as the amount of the dose is increased. On the other hand, the exchange bias field and thermoelectric voltage are not significantly affected by proton irradiation. This indicates that proton irradiation has more of an influence on the bulk property of the FM CoFeB layer and less of an effect on the IrMn/CoFeB interface.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.4B no.1
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• pp.6-11
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• 2004

The single phase switched reluctance motor (SRM) has many merits; simple structure and driving circuits, easy operation and speed control, and etc. This paper presents the torque characteristics of disk type single phase SRM by changing the salient pole lengths and pole arcs. The prototype single phase SRM has a three dimensional magnetic flux pattern because of its structure. That is, the radial and axial magnetic flux contributes to torque generation. Thus, 3D analysis is required for computation of its magnetic field. In this paper, 3D FEM is used for analyzing the magnetic flux distribution and magnetic co-energy.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.659-662
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• 1995

Co-ferrite ($CoO-Fe_{2}O_{3}$) thin films have been prepared by two ways of low temperature solid reaction including oxidation process, being based on $Co-layer/{\alpha}-Fe_{2}O_{3}$ films and $Co-layer/Fe_{3}O_{4}$ films. Magnetic properties of both Co-ferrite films have been measured and compared. The samples from $Co-layer/Fe_{3}O_{4}$ films have a large coercive force in the direction perpendicular and have a great poler kerr rotation angle at wavelength 700 nm than ones from $Co-layer/{\alpha}-Fe_{2}O_{3}$ films. The typical magnetic properties are as follows; saturation magnetization $4{\pi}Ms$, 2.9 kG; remnant magnetization $4{\pi}Mr$, 2.0 kG; coercive force Hc, 4.0 kOe; kerr rotation angle ${\PHI}k$, 0.39 deg($\lambda\;=\;700\;nm$); and initial magnetization energy E, $3.3\;{\times}\;10^6\;erg/\textrm{m}^3$, respectively.

• Journal of Magnetics
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• v.13 no.3
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• pp.97-101
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• 2008

We investigated the exchange bias fields at the NiFe/FeMn and FeMn/CoFe interfaces in 18.9-nm NiFe/15.0-nm FeMn/17.6-nm CoFe trilayer thin films as the annealing temperature was varied from room temperature to $250^{\circ}C$ in a vacuum for 1 hour in a magnetic field of 150 Oe. Interestingly, magnetic hysteresis (M-H) measurements showed that NiFe/FeMn/CoFe trilayer thin films exhibited a completely contrasting variation of the exchange bias fields at both the NiFe/FeMn and FeMn/CoFe interfaces with annealing temperatures. High-angle X-ray diffraction (XRD) measurements indicated the absence of any discernible effect of thermal treatment on the NiFe(111) and FeMn(111) peaks. The compositional depth profile obtained from X-ray photoelectron spectroscopy (XPS) results presented the asymmetric compositional depth profiles of the Mn and Fe atoms throughout the FeMn layer. We contend that this asymmetric compositional depth profile and the preferential Mn diffusion into the NiFe layer, compared to that into the CoFe layer, are conclusive experimental evidence of the contrasting variation of the exchange bias fields at two interfaces having a common polycrystalline FeMn(111) layer.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.86.2-86.2
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• 2011

We investigate the evolution of coronal loop emission in the context of the coronal magnetic field topology. New modeling techniques allow us to investigate the magnetic field structure and energy release in active regions (ARs). Using these models and high-resolution multi-wavelength coronal observations from the Transition Region and Coronal Explorer and the X-ray Telescope on Hinode, we are able to establish a relationship between the light curves of coronal loops and their associated magnetic topologies for NOAA AR 10963. We examine loops that show both transient and steady emission, and we find that loops that show many transient brightenings are located in domains associated with a high number of separators. This topology provides an environment for continual impulsive heating events through magnetic reconnection at the separators. A loop with relatively constant X-ray and EUV emission, on the other hand, is located in domains that are not associated with separators. This result implies that larger-scale magnetic field reconnections are not involved in heating plasma in these regions, and the heating in these loops must come from another mechanism, such as smallscale reconnections (i.e., nanoflares) or wave heating. Additionally, we find that loops that undergo repeated transient brightenings are associated with separators that have enhanced free energy. In contrast, we find one case of an isolated transient brightening that seems to be associated with separators with a smaller free energy.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.5
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• pp.562-570
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• 2016

At the carbon dioxide capture process using the aqueous amine solution, degradation of absorbents is main factor to reducing the process performance. Also, degradation mechanism of absorbent is important for understanding the environmental risk, route of degradation products, health risk etc. In this study, the degradation products of MEA were studied to clarify mechanism in thermal degradation process. The degradation products were analyzed using a $^1H$ NMR (nuclear magnetic resonance) and $^{13}C$ NMR. The analysis methods used in this study provide guidelines that could be used to develop a degradation inhibitor of absorbent and a corrosion inhibitor.

• Journal of the Korean Magnetics Society
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• v.11 no.5
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• pp.184-188
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• 2001

Using a DC-sputter and changing the substrate temperature to room temperature and 200$\^{C}$, we manufactured each Co-22%Cr alloy thin-films, which has a uniform micro-structure at room temperature, and a fine self-organized nato structure (SONS) at the inside of the grain at the elevated temperature. We also investigated the microstructure and domain structure using a transmission electron microscope (TEM) and a magnetic force microscope (MFM). We managed to corrode selectively Co-enriched phase, then investigate the microstructure using a TEM. We found that it has a uniform composition when it is manufactured at room temperature, but, we found that it has a unique microstructure, which has a plate-like fine Co-enriched phase, with the formation of SONS at the inside of the grain at the elevated temperature. In MFM characterization, we found maze-type domains at the period of 5000 when the substrate temperature maintains at room temperature. We define that the maze-type domain has a disadvantage at the high density recording because it generates noises easily as the exchange coupling energy between the grains is big. On the other hand, there is only a fine domain structure at the period of 500 when the substrate temperature maintains at 200 $\^{C}$. We define that the fine domain structure has an advantage at the high density magnetic recording because it has thermal stability due to small exchange coupling energy.