• KEPCO Journal on Electric Power and Energy
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• v.1 no.1
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• pp.15-20
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• 2015

To examine the magnetic shielding effect for carbon-based materials at extremely low frequencies (60 Hz), two types of carbon black (Super-P and Denka Black) and a natural graphite (HC-198) were mixed into organic binder at 10 wt.% to produce a coating solution, and a powder coating with varying thickness was applied on an aluminum disk measuring 88 mm in radius. A device was developed to measure the sheielding effect at extremely low frequencies. A closed circuit was achieved by connecting a transformer and a resistor. The applied voltage was fixed at 65 V, and the magnetic field was measured to being the range of 4.95~5.10 mG. Depending on the thickness of the coating layer, the magnetic field showed a decreasing trend. The maximum decrease in the magnetic field of 38.3% was measured when natural graphite was coated with specimens averaging $455{\mu}m$. This study confirmed that carbon-based materials enable magnetic shielding at extremely low frequencies, and that the magnetic shielding effect can be enhanced by varying the coating thickness.

• Journal of Magnetics
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• v.9 no.4
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• pp.116-120
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• 2004

Hexagonal barium-ferrite ($BaFe_{12}O_{19}$, magnetoplumbite structure; BaM) film with perpendicularly c-axis orientation was successfully deposited on (100) silicon substrates with an MgO (111) underlayer by rf diode sputtering and in-situ heating at $920^{\circ}C$. The magnetic and structural properties of 0.27 ${\mu}m$ thick BaM films on MgO (111) underlayers were compared to films of the same thickness deposited onto single-crystal MgO (111) and c-plane ($000{\ell}$) sapphire ($Al_2O_3$) substrates by vibrating sample magnetometry (VSM), x-ray diffractometer (XRD), and atomic force microscopy (AFM). The thickness dependence of MgO (111) underlayers on silicon wafer was found to have a large effect on both magnetic and structural properties of the BaM film. The thickness of 15 nm MgO (111) underlayers produced BaM films with almost identical magnetic and structural properties as the single-crystal substrates; this can be explained by the lower surface roughness for thinner underlayer thicknesses. The magnetization saturation ($M_s$) and the ratio $H_{cII}/H_{c{\bot}}$ for the BaM film with a 15 nm MgO (111) underlayer is 217 emu/cc and 0.24, respectively. This is similar to the results for the BaM films deposited on the single-crystal MgO (111) and sapphire substrates of 197 emu/cc and 0.10, 200 emu/cc and 0.12, respectively. Therefore, the proposed MgO (111) underlayer can be used in many applications to promote c-axis orientation without the cost of expensive substrates.

• Korean Journal of Materials Research
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• v.26 no.11
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• pp.623-627
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• 2016

$La_{1-x}Ba_xMnO_3$ (x = 0.30, 0.35 and 0.40) samples have been prepared by solid-state reaction method. The X-ray diffraction (XRD) study showed that all the samples crystallized in a rhombohedral structure with an R-3c space group. Variation of the magnetization as a function of the temperature and applied magnetic field was carried out. All the samples revealed ferromagnetic to paramagnetic (FM-PM) phase transition at the Curie temperature $T_C{\sim}342K$. The magnetic entropy change was also studied through examination of the measured magnetic isotherms M(H, T) near $T_C$. The magnetocaloric effect was calculated in terms of the isothermal magnetic entropy change. The maximum entropy change reaches a value of 1.192 J/kgK under a magnetic field change of 2.5T for the $La_{0.6}Ba_{0.4}MnO_3$ composition. The relative cooling power (RCP) is 79.31 J/kg for the same applied magnetic field.

• Journal of Magnetics
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• v.11 no.1
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• pp.30-35
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• 2006

A thorough study about the influences of Mn substitution for Fe on the microstructure and magnetic characteristics of $Fe_{73.5-x}Mn-{x}Si_{13.5}B_{9}Nb_{3}Cu_1$ (x = 1, 3, 5) alloys prepared by the melt-spinning technique has been performed. Nanocomposites composed of nanoscale $(Fe,Mn)_{3}Si$ magnetic phase embedded in an amorphous matrix were obtained by annealing their amorphous alloys at $535^{\circ}C$ for 1 hour. The addition of Mn causes a slight increase in the mean grain size. The Curie temperatures of the initial amorphous phase and of the nanocrystals phase decreased, while the Curie temperature of the remaining amorphous phase remained nearly constant with increasing Mn content. Soft magnetic properties of the crystallized samples have been significantly improved by a proper thermal treatment. Accordingly, the giant magnetoimpedance effect is observed and ascribed to the increase of the magnetic permeability, and the decrease of the coercivity of the samples. The increased magnetic permeability is resulted from a decrease in the magnetocrystalline anisotropy and saturation magnetostriction.

• Journal of Magnetics
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• v.16 no.4
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• pp.363-367
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• 2011

We have designed, fabricated and demonstrated a novel micro-system for programmable magnetic actuation using magnetic elliptical pathways on Si substrates. Lithographically patterned soft NiFe ellipses are arranged sequentially perpendicular to each other as stepping stones for the transport of magnetic beads. We have measured the magnetization curve of the ellipsoid ($9\;{\mu}m{\times}4\;{\mu}m{\times}0.1\;{\mu}m$) elements with respect to the long and short axes of the ellipse. We found that the magnetization in the long axis direction is larger than that in the short axis direction for an applied field of ${\leq}$ 1,000 Oe, causing a force on carriers that causes them to move from one element to another. We have successfully demonstrated a micro-system for the magnetic actuation of biomolecule carriers of superparamagnetic beads (Dynabead$^{(R)}$ 2.8 ${\mu}m$) by rotating the external magnetic field. This novel concept of magnetic actuation is useful for future integrated lab-on-a-chip systems for biomolecule manipulation, separation and analysis.

• Proceedings of the Korean Magnestics Society Conference
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• 2007.05a
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• pp.279.2-279.2
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• 2007

• Journal of Magnetics
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• v.9 no.4
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• pp.109-112
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• 2004

The HDDR (Hydrogenation-Disproportionation-Desorption-Recombination) process is a special method to produce anisotropic NdFeB powders for bonded magnet. The effect of the modified HDDR process on magnetic properties of $Nd_2Fe_{14}B$-based magnet with several composition $Nd_{11.2}Fe_{66.5-x}Co_{15.4}B_{6,8}Zr{0.1}Ga_x(x=0{\sim}1.0)$ and that of microelement Ga, disproportional temperature and annealing temperature on $_jH_c$, grain size were investigated in order to produce anisotropic powder with high magnetic properties. It was found that modified HDDR process is very effective to enhance magnetic properties and to fine grain size. The addition of Ga could change disproportionation character remarkably of the alloy and could improve magnetic properties of magnet powder. Increasing annealing temperature induces significant grain growth. And grain size produced by modified HDDR process is significantly smaller than those produced by conventional HDDR process.

• Proceedings of the Korean Magnestics Society Conference
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• 2007.05a
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• pp.143.2-143.2
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• 2007

• Proceedings of the Korean Magnestics Society Conference
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• 2003.06a
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• pp.92-93
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• 2003

• Proceedings of the Korean Magnestics Society Conference
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• 2008.12a
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• pp.291.1-291.1
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• 2008