• Proceedings of the Korean Magnestics Society Conference
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• 2007.12a
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• pp.64-66
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• 2007

• Proceedings of the Korean Magnestics Society Conference
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• 2002.12a
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• pp.214-215
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• 2002

High saturation magnetization (B$\_$s/) and excellent high frequency characteristics of magnetic thin films has been recognized as the most important requirement for further miniaturization and higher frequency operation in magnetic devices, such as magnetic heads and magnetic sensors. Up to now, Fe-X-N (X =Ti, Hf, and Al etc.) films with B$\_$s/ of 15 ∼ 19 kG and coercivity (H$\_$c/) of 0.5 ∼ 5.0 Oe have been successfully fabricated and proven to satisfy various requirements as a potential candidate for thin film head materials. (omitted)

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.12
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• pp.2270-2275
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• 2011

The sintering behavior and microwave properties of ferrite ($Ba_3Co_{2-2x}Zn_{2x}Fe_{24}O_{41}$ ceramics) were investigated for microwave applications. Also PIFA type antenna with ferrite was simulated. All samples were prepared by the solid state reaction method and sintered at $1350^{\circ}C$. All ceramics had relatively density above of 92% compare with theoretical density of $Ba_3Co_2Fe_{24}O_{41}$ ceramics. From the XRD pattens, the Z-type phase was existed as main phase in $Ba_3Co_{2-2x}Zn_{2x}Fe_{24}O_{41}$ ceramics. The permittivity and permeability of $Ba_3Co_{2-2x}Zn_{2x}Fe_{24}O_{41}$ ceramics were increased with Zn additions and decreased rapidly over frequency of 200~600 MHz. Several PIFA type antennas with ferrite and FR4 were simulated. All antenna structure had return loss of less than -10 dB at each resonant frequency. Simulated antenna using both ferrite and FR4 showed size reduction of 25% without a significant decrement of efficiency.

• Proceedings of the Korean Magnestics Society Conference
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• 2014.05a
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• pp.122-124
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• 2014

• 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.

• Journal of Magnetics
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• v.15 no.1
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• pp.25-28
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• 2010

This study examined the crystallographic and magnetic properties of vanadium-substituted lithium cobalt titanium ferrite, $Li_{0.7}Co_{0.2}Ti_{0.2}V_{0.2}Fe_{1.7}O_4$. Ferrite was synthesized using a conventional ceramic method. The samples annealed below $1040^{\circ}C$ showed X-ray diffraction peaks for spinel and other phases. However, the sample annealed above $1040^{\circ}C$ showed a single spinel phase. The lattice constant of the sample was $8.351\;{\AA}$, which was relatively unaffected by vanadium-substitution. The average grain size after vanadium-substitution was $13.90\;{\mu}m$, as determined by scanning electron microscopy. The M$\ddot{o}$ssbauer spectrum could be fitted to two Zeeman sextets, which is the typical spinel ferrite spectra of $Fe^{3+}$ with A and B sites, and one doublet. From the absorption area ratio of the M$\ddot{o}$ssbauer spectrum, the cation distribution was found to be ($Co_{0.2}V_{0.2}Fe_{0.6})[Li_{0.7}Ti_{0.2}Fe_{1.1}]O_4$. Vibrating sample magnetometry revealed a saturation magnetization and coercivity of 36.9 emu/g and 88.6 Oe, respectively, which were decreased by vanadium-substitution.

• Korean Chemical Engineering Research
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• v.56 no.5
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• pp.641-646
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• 2018

Sodium borohydride, $NaBH_4$, shows a number of advantages as hydrogen source for portable proton exchange membrane fuel cells (PEMFCs). Properties of $NaBH_4$ hydrolysis reaction using activated carbon supported Co-B/C, Co-P-B/C catalyst were studied. BET surface area of catalyst, yield of hydrogen, effect of $NaBH_4$ concentration and durability of catalyst were measured. The BET surface area of carbon supported catalyst was over $500m^2/g$ and this value was 2~3 times higher than that of unsupported catalyst. Hydrogen generation of activated carbon supported catalyst was more stable than that of unsupported catalyst. The activation energy of Co-P-B/C catalyst was 59.4 kJ/mol in 20 wt% $NaBH_4$ and 14% lower than that of Co-P-B/FeCrAlloy catalyst. Catalyst loss on activated carbon supported catalyst was reduced to about 1/3~1/2 compared with unsupported catalyst, therefore durability was improved by supporting catalyst on activated carbon.

• Journal of the Korean Magnetics Society
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• v.10 no.5
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• pp.220-224
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• 2000

Ultra-fine $Co_{1+x}$F $e_{2-}$2x/ $Ti_{x}$ $O_4$ferrite powders have been prepared by the sol-gel method. The crystallographic and magnetic properties of the sample have been investigated by means of x-ray diffraction, Mossbauer spetroscopy and vibrating sample magnetometry. The formation of nano crystallized particles is confirmed. The x-ray diffractions of all samples with various compositions clearly indicate the presence of spinel structure. The Mossbauer spectra could be fitted as the superposition of two sextets due to F $e^{3+}$ A-site and B-site. The IS and QS values nearly constant with substituted Co-Ti contents, whereas $H_{hf}$ of B-site decreases with increasing Co-Ti substitution in $Co_{1+x}$F $e_{2-}$2x/ $Ti_{x}$ $O_4$. The magnetic behaviour of powders shows that the saturation magnetization and the coercivity decrease with increasing x in $Co_{1+x}$F $e_{2-}$2x/ $Ti_{x}$ $O_4$.$.X>.

• Journal of the Korean Institute of Telematics and Electronics
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• v.14 no.3
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• pp.25-31
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• 1977

Fe V spinels were prepared by sintering the well-ground stoichiometric mixtures of Fe O and V O at 1,10$0^{\circ}C$ under H -CO atmosphere. The activation energy for electrical conduction decreases with increasing amount of iron. The tendency of activation energy depending on the amount of iron contained clarifies that the electrical condction of the spinel is mainly due to electron hopping between Fe and Fe ions at B sites. In the experiment for negative resistance characteristics, the threshold voltage (Vth) for the samples is related to ambient temperature, thickness and raising rate of applied voltage. Vth decreases as temperature increases while Vth increases linearly with thickness and Vth increases linearly with the raising rate of applied voltage in semi-logarithmic scale. These results lead to a conclusion that current paths mainly formed by thermal breakdown are ascribed to the negative resistance phenomena. Applying this property, these vanadium iron spinels may be used for switching elements.

• Journal of Welding and Joining
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• v.25 no.3
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• pp.51-56
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• 2007

A $CO_2$ laser overlay was conducted by using a Fe-based powder on the AC2B aluminum substrate. Cracks and intermetallic compounds (IMC) were observed inconsistently along the interface between the overlay and post-molten layer. A scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) detected some Fe-rich IMC ($Fe_3Al$, FeAl) as well as the brittle Al-rich IMC ($Fe_2Al_5,\;FeAl_3$). Micro vickers hardness proved the formation of Al-rich IMC ($FeAl_3$) along the interface by showing HV0.1 $800{\sim}900$. Furthermore, nano indentation was successfully applied to investigate the behavior of IMC more precisely than the micro vickers hardness.