• Journal of the Korean Magnetics Society
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• v.4 no.3
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• pp.219-225
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• 1994

The alignment of Sr-ferrite magnetic powders, which is usually related to the fluidity and the applied magnetic field, is investicated in the anisotropic Sr-ferrite / resin-bonded permanent magnets. The magnetic powder alignment is observed to increase with the applied magnetic field and the fluidity which is a function of molding temperature and powder packing ratio. The best magnetic powder alignment is achieved at the following conditions; Sr-ferrite packing ratio of 56vol%, apparent viscosity of about 3000 poise in $1000sec^{-1}$ shear rate, and applied magnetic field of about 5kOe. The degree of preferred orientation of the magnetic powders in the field direction, as determined by the dc hysterisis graphs, is 84~85% (0.84~0.85). This result is in agreement with the value of 0.85 obtained by the X-ray experiments in the $2{\theta}$ range of ${23~40}^0$. The best magnetic properties obtained are:2.2kG of remanent flux density, 2.2MGOe of maximum energy product.

• 연구논문집
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• s.34
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• pp.121-129
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• 2004

The influence of powder size and ball-milling time on the magnetic properties of $Fe_{73}Si_{16}B_7Nb_3Cu_1$ nanocrystalline alloy powder was investigated. Flake-shaped powders were produced by pulverizing the ribbons annealed at $550^\circC$ for 1 hour. The powders were classified and consolidated into core shapes at a pressure of 18ton/$cm^2$. The initial permeability at 100kHz of the inductor core produced using $53-75\mum$ powders showed the highest value although its consolidated density showed the lowest one. The reason for the result is due to the cracking of the particles larger than $75\mum$ during the consolidation process. The ball-milling of powders for 2-4 hours improved the consolidation density and the initial permeability of the cores. The intrinsic coercivity of the powder decreased as well, resulting from the stress relief of the powder by a short-time milling.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1167-1168
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• 2006

In this study, the pure iron powder was treated with aqueous phosphoric acid to produce phosphate insulating layer on the surface. After drying the powder, it was compacted in a mold with a diameter of 20mm at 800MPa. The powder compacts were then heat treated at $500^{\circ}C$ for 1 hour. The results showed that insulated iron powder was obtained with uniform phosphate layer by chemical reaction. With increased amount of phosphate layer, the core loss and density of compacts were decreased. It was also found that the addition of ethyl alcohol during insulating reaction resulted in improved core loss value.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1196-1197
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• 2006

FePt binary-alloy nanopowder has been successfully synthesized by chemical vapor condensation process with two metal organic precursors, i.e., iron pentacarbonyl and platinum acetylacetonate. Average particle size of the powder was less than 50 nm with very narrow size distribution, revealing high dispersion capability. Characteristics of the powder could be controlled by changing process parameters such as reaction temperature, chamber pressure, as well as gas flow rate. Magnetic properties of the synthesized FePt nanopowder were investigated and analyzed in terms of the powder characteristics.

• Journal of Powder Materials
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• v.13 no.3 s.56
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• pp.217-222
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• 2006

The relationship between electrical properties of superconductor and externally applied magnetic field was studied to develop a magnetic field sensor. The electrical resistance of the superconductor was increased by applying external magnetic field and even after removal of the magnetic field. This behavior was related to the magnetic flux trapped in the superconductor, which penetrated through the material by the external magnetic field. Some portion of the superconductor was changed to a normal state by the trapped magnetic flux. The appearance of the normal state yielded to enhance the electrical resistance.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.04a
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• pp.83-87
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• 2002

In order to improve the capability of magnetic circuit, magnetic materials are used for all kinds of electromagnetic energy-conversion devices. This paper presents the analysis method considering magnetic properties of the magnetic material and analyzes that the effects of magnetic materials. In addition, it is described that the requirements of magnetic materials for the improvement of electric machines. Several application examples using a metal powder in electromagnetic energy conversion devices is introduced.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2001.04a
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• pp.19-19
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• 2001

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.04a
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• pp.11-12
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• 2006

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1998.10b
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• pp.40-40
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• 1998

• Transactions of the Korean hydrogen and new energy society
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• v.25 no.6
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• pp.594-601
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• 2014

Rare-earth (RE) nitrides can be used as magnetocaloric materials in low temperature. They exhibit ferromagnetism and have Curie temperature in the region from 6 to 70 K. In this study, Holmium nitride (HoN) nano particles were prepared through plasma arc discharge technique and their magnetocaloric properties were studied. Nitrogen gas ($N_2$) was employed as an active element for arc discharge between two electrodes maintained at a constant current. Also, it played an important role not only as a reducing agent but also as an inevitable source of excited nitrogen molecules and nitrogen ions for the formation of HoN phase. Partial pressure of $N_2$ was systematically varied from 0 to 28,000 Pa in order to obtain single phase of HoN with minimal impurities. Magnetic entropy change (${\Delta}S_m$) was calculated with data set measured by PPMS (Physical Property Measurement System). The as-synthesized HoN particles have shown a magnetic entropy change ${\Delta}S_m$) of 27.5 J/kgK in applied field of 50,000 Oe at 14.2 K thereby demonstrating its ability to be applied as an effective magnetic refrigerant towards the re-liquefaction of hydrogen.