• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.176-176
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• 2003

강자성 반도체(DMS)는 반도체에 전이금속을 doping함으로써 반도체의 전자 수송 특성과 전이 금속 이온에 의한 자기적 특성을 동시에 발현할 수 있도록 설계된 물질로서 '스핀 전자공학'의 구현을 위해 현재 활발히 연구되고 있는 분야이다. 특히 높은 전기 전도도와 투명 광 특성을 가지는 ZnO계는 전이금속을 첨가 할 경우 상온에서도 강자성 특성을 보일 것이라는 연구가 발표 된 이후 큰 주목을 받고 있으며, 실제로 Tc가 상온 이상인 결과들이 최근 발표되고 있다. 그러나 PLD에 의해 증착 된 Co-doped ZnO 경우 강자성 물성의 재현성이 아주 낮은 것으로 알려져 있는 둥 강자성 발현의 기원이 아직도 명확히 규명되지 못한 상태이다. 이에 본 연구에서는 Co-doped ZnO 계의 강자성 발현의 기원을 밝히고자 고상 반응법을 이용하여 다결정계를 제조한 후 X-선 회절 분석과 Raman 분광법을 이용하여 제2차상의 존재 유무 및 Co 이온의 치환 정도를 분석하였다. 다음으로 방사광 EXAFS 분석을 행하여 ZnO내에서의 Co 이온의 원자가 상태를 분석하고, PPMS를 사용 M-T curve를 측정/분석함으로써 강자성 발현의 기원을 규명하고자 하였다.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.1 s.343
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• pp.7-12
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• 2006

In this study, we developed irreversible and stable micro-size ferromagnetic structures utilizing hydrogenation and electron-beam lithography processes. The compositionally modulated (CM) Fe-Zr thin films that had average compositions $Fe_XZr_{100-x}$ with $x=65-85\%$ modulation periods of similar to 1 nm, and total thicknesses of similar to 100 m were prepared. The magnetic properties of CM Fe-Zr thin films were measured using a SQUID magnetometer, VSM and B-H loop tracer. After hydrogenation, the CM films exhibited larger magnetic moment increases than similar homogeneous alloy films for all compositions and かey showed largest increase in $Fe_{80}Zr_{20}$ composition. After aging in air at $300^{\circ}K$ the hydrogenated $Fe_{80}Zr_{20}$ CM films showed much larger magnetic moment increases, indicating that they relax to a stable, irreversible, soft magnetic state. The selective hydrogenation through electron-beam lithographed windows were performed after the circle shaped windows were prepared on $Fe_{80}Zr_{20}$ CM films by electron beam lithography. The hydrogenation through electron-beam resist and W lithographic techniques give a $49\%$ magnetic moment increase. This method can be applied to nano scale structures.

• Composites Research
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• v.20 no.5
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• pp.43-48
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• 2007

The absorption and the interference shielding of electromagnetic wave have been very important issues for commercial and military purposes. The stealth technique is one of the most typical applications of electromagnetic wave absorption technology. This study has started for the development of composite fillers containing dielectric and magnetic lossy materials. To improve the electromagnetic characteristics of conductive nano fillers, carbon nanofibers (CNFs) with nickel-phosphorous (Ni-P) or nickel-iron (Ni-Fe) have been fabricated by the electroless plating process. Observations by the electron microscopy (SEM/TEM) and element analyzer (EDS/ELLS) showed the uniform Ni-P and Ni-Fe coated CNFs. The compositions of the plating layers were about Ni-6wt%P and Ni-70wt%Fe, respectively. The average thicknesses of the plating layers were about $50\;{\sim}\;100\;nm$.

• Journal of the Korean Magnetics Society
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• v.17 no.4
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• pp.147-151
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• 2007

We have investigated the half-metallicity and magnetism for the Heusler ferromagnet $Co_2$ZrSi interfaced with semiconductor ZnTe along the (001) plane by using the full-potential linearized augmented plane wave (FLAPW) method. We considered low types of possible interfaces: ZrSi/Zn, ZrSi/Te, Co/Zn, and Co/Te, respectively. From the calculated density of states, it was found that the half-metallicity was lost at all the interfaces, however for the Co/Te system the value of minority spin density of states was close to zero at the Fermi level. These facts are due to the interface states, appeared in the minority spin gap in bulk $Co_2$ZrSi, caused by the changes of the coordination and symmetry and the hybridizations between the interface atoms. At the Co/Te interface, the magnetic moments of Co atoms are 0.68 and $0.78{\mu}_B$ for the "bridge" and "antibridge" sites, respectively, which are much reduced with respect to that ($1.15{\mu}_B$) of the bulk $Co_2$ZrSi. In the case of Co/Zn, Co atoms at the "bridge" and "antibridge" sites have magnetic moments of 1.16 and $0.93{\mu}_B$, respectively, which are almost same or slightly decreased compared to that of the bulk $Co_2$ZrSi. On the other hand, for the ZrSi/Zn and ZrSi/Te systems, the magnetic moments of Co atoms at the sub-interface layers are in the range of $1.13{\sim}1.30\;{\mu}_B$, which are almost same or slightly increased than that of the bulk $Co_2$ZrSi.

• Journal of the Korean Magnetics Society
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• v.19 no.2
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• pp.57-61
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• 2009

$MnFe_2O_4$ nanoparticles have been prepared by a sol-gel method. The structural and magnetic properties have been investigated by XRD, SEM, and $M{\ddot{o}}ssbauer$ spectroscopy, VSM. $MnFe_2O_4$ powder that was annealed at $250^{\circ}C$ has spinel structure and behaved superparamagnetically at room temperature. $MnFe_2O_4$ annealed at 400 and $500^{\circ}C$ has a typical spinel structure and is ferrimagnetic in nature. The estimated size of superparammagnetic $MnFe_2O_4$ nanoparticle is around 17 nm. The hyperfine fields of the A and B patterns at 4.2 K were found to be 508 and 475 kOe, respectively. The blocking temperature ($T_B$) of superparammagnetic $MnFe_2O_4$ nanoparticle is about 120 K. The magnetic anisotropy constant and relaxation time constant of $MnFe_2O_4$ nanoparticle were calculated to be $4.9{\times}10^5erg/cm^3$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.541-545
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• 2003

Mn-Zn 페라이트의 자심재료가 전자기 부품용 응용될 때, 소형화와 고효율화를 이루기 위한 공정변수에 따른 전자기적 특성변화를 고찰하였다. ZnO 의 몰비가 11 mole일 때, 가장 우수한 특성을 나타내었으며, $SiO_2$와 CaO는 입계 저항층 형성을 통한 손실을 감소시키고, 이로 인해 성능지수는 증가하여 $100\;kHz\;{\sim}\;200\;kHz$ 범위에서 최대값을 나타내어 전자기적 효율이 극대화되었다. 산소분압의 제어는 승온과정부터 산소분압을 제어시켜주어야만 Zn-loss 현상의 증가와 $Fe^{2+}$ 이온 농도의 감소 및 $Fe^{2+}-\;Fe^{3+}$ 이온간의 호핑(hoping)현상 등에 의한 손실을 최소화할 수 있으며, 높은 투자율을 얻을 수 있었다. 그리고 소결 또는 냉각 중 평형 산소분압이 유지되지 못하면 다량의 결함이 출현하게 되고, 특히 $600^{\circ}C$ 이하에서 스피넬 상의 분해-산화반응이 일어나면서 미세구조 상에 결함으로 남게 되어 전자기적 특성이 저하되었다.

• Journal of the Korean Magnetics Society
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• v.18 no.4
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• pp.131-135
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• 2008

The electronic structures, magnetism, and half-metallicity of the full-Heusler $Co_2TiSn$(001) surfaces have been investigated by using the all-electron full-potential linearized augmented plane wave method within the generalized gradient approximation. We have considered both of the Co atoms terminated(Co-term) and the TiSn atoms terminated(TiSn-term) surfaces. From the calculated density of states, we found that the half-metallicity was destroyed at the surface of the Co-term, while the half-metallicity was retained at the TiSn-term. For the surface of the Co-term, due to the reduced coordination number the occupied minority d-states were shifted to high energy regions and that cross the Fermi level, thus destroy the surface half-metallicity. On the other hand the surface states at the surface of the TiSn-term were located just below the Fermi level, which reduces the minority spin-gap with respect to that of the center layer. The calculated magnetic moment of the surface Co atom for the Co-term was increased by 10 % to 1.16 ${\mu}_B$ with respect to that of the inner-layers, while the magnetic moment of the subsurface Co atom in the TiSn-term has almost same value of the innerlayers(1.03 ${\mu}_B$).

• Proceedings of the KIPE Conference
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• 2011.07a
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• pp.308-309
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• 2011

최근 PDP와 LCD등의 FPD용(用) 전원 시스템에 고효율화, 고밀도화 및 Slim화를 위한 전원 회로 기술이 요구됨에 따라 이를 실현하기 위해서는 전원 회로를 구성하는 각 컨버터의 최적 Topology 확보뿐만 아니라, 전원 회로에 사용되는 부품들에 대한 차별화된 핵심 부품 기술 확보가 필수적이다. 이러한 요구에 부합하기 위해서 FPD용(用) 전원에 적용되는 자성부품구조도 기존의 성능을 유지하면서 박형화, 저비용화 및 자동 권선화를 구현할 수 있는 방안에 대한 연구가 필요하다. 본 논문에서는 LED-TV용 전원장치의 EMI Filter부의 개발사례 및 특히 EMI Filter부의 대책부품 중에 자동권선형 공통모드 초크의 개발동향 및 사례에 대해서 소개하고자 한다.

• Journal of the Korean Magnetics Society
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• v.5 no.3
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• pp.185-190
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• 1995

Rare earth-aluminum intermetallic compounds $RAI_{2}$ (R ; Lu, Ce, Gd) are prepared by the arc-melt method and the magnetic properties and electronic structures are investigated by magnetic susceptiptibiliy measurements using SQUID magnetometer. The magnetic suceptibiliyof $LuAl_{2}$ is weakly temperature dependent and shows a Pauli susceptibility of $10.1{\times}10^{-5}$ emu/mol, which means 3.2 states/eV/formula unit. On the other hand, the susceptibility data of $CeAl_{2}$ and $GdAl_{2}$ show a Curie-Weiss behavior for paramagnets. The magnetization data at low temperatures confirm that $CeAl_{2}$ undergoes an antiferromagnetic phase transition near 4 K whereas $GdAl_{2}$ a ferromagnetic transition at 170 K. The distinctive magnetic behaviors of $RAI_{2}$ originate from the different 4f band filling.

• Journal of the Korean Magnetics Society
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• v.18 no.5
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• pp.195-199
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• 2008

Composites of $Fe_{93.5}Si_{6.5}$ powder and epoxy were prepared using a thermal curing process. Scanning electron microscope (SEM), vibrating sample magnetometer (VSM) and network analyzer were used to analyze the structure, electromagnetic properties and microwave absorption of the composites. Results show that the saturation magnetization depends on the fraction of the $Fe_{93.5}Si_{6.5}$ powder in the composite, which affects initial permeability. It is believed that the eddy current loss is a dominant factor over 1 GHz and that the resonance frequency of the composite decreases with increasing fractions of $Fe_{93.5}Si_{6.5}$ powder. Finally, reflection loss was calculated from the permeability and permittivity of these composites. Composite with 50 wt.% $Fe_{93.5}Si_{6.5}$ powder fractions and 5 mm thickness showed reflection loss below -20 dB from 3.66 GHz to 4.16 GHz. Therefore, it is believed that thin Fe-Si/epoxy composites may be a good candidate for microwave absorption application.