• 한국재료학회지
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• 제28권3호
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• pp.159-165
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• 2018

In order to increase the efficiency of the sputtering method widely used in thin film fabrication, a dc sputtering apparatus which supplies both high frequency and magnetic field from the outside was fabricated, and cobalt thin film was fabricated using this apparatus. The apparatus can independently control the applied voltage, the target-substrate distance, and the target current, which are important parameters in the sputtering method, so that a stable glow discharge is obtained even at a low gas pressure of $10^{-3}$ Torr. The fabrication conditions using the sputtering method were mainly performed in $Ar+O_2$ mixed gas containing about 0.6 % oxygen gas under various Ar gas pressures of 1 to 30 mTorr. The microstructure of Co thin films deposited using this apparatus was examined by electron diffraction pattern and X-ray techniques. The magnetic properties were investigated by measuring the magnetization curves. The microstructure and magnetic properties of Co thin films depend on the discharge gas pressure. The thin film fabricated at high gas pressure showed a columnar structure containing a large amount of the third phase in the boundary region and the thin film formed at low gas pressure showed little or no columnar structure. The coercivity in the plane was slightly larger than that in the latter case.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 춘계학술발표강연 및 논문개요집
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• pp.239-239
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• 2003

As a result of the recent miniaturization and enhancement in the performance of thin film inductors and thin film transformers, there are increased demands for the thin films with a high magnetic permeability in the high frequency range, a high saturation magnetization, a high electrical resistivity, and a low coercive force. In order to improve high frequency properties, we will investigate anisotropy field by shape and size of pattern. The Fe-Al-O thin films of 16mm diameter and 1$\mu\textrm{m}$ thickness were deposited on Si wafer, using RE magnetron reactive sputtering technique with the mixture of argon and oxygen gases. The fabricating conditions are obtained in the working partial pressure of 2m Torr, O$_2$ partial Pressure of 5%, Input power of 400w, and Al pellets on an Fe disk with purity of 99.9%. For continuous thin film is the 4Ms of 19.4kG, H$\sub$c/ of 0.6Oe, H$\sub$k/ of 6.0Oe and effective permeability of 2500 up to 100MHz. In this work, we expect to enhanced effect of magnetic anisotropy on patterned of Fe-Al-O thin films.

• Advances in environmental research
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• 제4권2호
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• pp.69-81
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• 2015

A new magnetite-silica core/shell nanocomposite ($Fe_3O4@nSiO_2@mSiO_2$) was synthesized and functionalized with trimethylchlorosilane (TMCS). The prepared nanocomposite was used for the removal of diesel oil from aqueous media. The characterization of magnetite-silica nanocomposite was studied by X-ray diffraction (XRD), Fourier transform infrared (FTIR), transmission electron microscopy (TEM), surface area measurement, and vibrating sample magnetization (VSM). Results have shown that the desired structure was obtained and surface modification was successfully carried out. FTIR analysis has confirmed the presence of TMCS on the surface of magnetite silica nanocomposites. The low- angle XRD pattern of nanocomposites indicated the mesoscopic structure of silica shell. Furthermore, TEM results have shown the core/shell structure with porous silica shell. Adsorption kinetic studies indicated that the nanocomposite was able to remove 80% of the oil contaminant during 2 h and fit well with the pseudo-second order model. Equilibrium studies at room temperature showed that the experimental data fitted well with Freundlich isotherm. The magnetic property of nanocomposite facilitated the separation of solid phase from aqueous solution.

• 한국세라믹학회지
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• 제31권12호
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• pp.1501-1506
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• 1994

The precipitate of FeCl2.4H2O and NaOH, Fe(OH)2 was rapidly made to oxidize by H2O2 to prepare $\delta$-FeOOH. The particle size, surface and morphology of $\delta$-FeOOH, and the shape and structure of thermally decomposed $\delta$-FeOOH were investigated by the use of high resolution STEM. $\delta$-FeOOH prepared under the condition of reaction temperature of Fe(OH)2 at 4$0^{\circ}C$, [OH-][Fe2+]=5 and aging time of 2 hr Fe(OH)2, had 630$\AA$ mean particle size, 4~5 aspect ratio, 20.8 emu/g saturation magnetization and 210 Oe coercivity. The edges of $\delta$-FeOOH were inclined to (001) about 41$^{\circ}$, 60$^{\circ}$ and coincident with (102), (101) respectively. When $\delta$-FeOOH was thermally decomposed at 25$0^{\circ}C$ for 2 hr in vacuo, which had micropores of 0.9 nm thickness and crystallites of 2.4 nm thickness. (001)hex, [10]hex. of $\delta$-FeOOH parallel with (001)hex, [100]hex. of $\alpha$-Fe2O3 respectively. This showed three dimensional topotaxial structure transition, which was investigated by SADP (Selected Area Diffraction Pattern) of STEM.

• 한국세라믹학회지
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• 제29권3호
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• pp.195-201
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• 1992

It had been studied the structure and the magnetic properties of singel phase Co2Y(Ba2Co2Fe12O22) powder, one of the hexagonal ferrite. The material was successfully prepared by a commercially applicable coprecipitation method. Adding asqueous solution of BaCl2, CoCl2 and FeCl2(Ba2+:Co2+:Fe2+=1:1:6 in mole ratio) to a mixture of NaOH and hydrogen peroxide solution, coprecipitate was formed with rapid oxidation of ferrous to ferric ion. The coprecipitate transformed to single phase Co2Y powder at heat treatment temperatures as low as 900$^{\circ}C$. The shape of Co2Y particles obtained at 900$^{\circ}C$ was hexagonal plate-like (diameter∼$\mu\textrm{m}$, aspect ratio>10). The structure of the Co2Y was refined by a Rietveld analysis of the measured X-ray diffractogram. The lattice parameters are ao=5.8602${\AA}$ and co=43.512${\AA}$. Co2Y is a soft magnetic material with saturation magnetization 30 emu/g and coecivity 170 . A standard X-ray diffraction pattern for Co2Y is proposed as well.

• Journal of Magnetics
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• 제14권2호
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• pp.75-79
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• 2009

Nickel (Ni) and ferrite ($Fe_3O_4$, $NiFe_2O_4$) nanoparticles were synthesized by LGC using both wire feeding (WF) and micron powder feeding (MPF) systems. Phase evolution and magnetic properties were then investigated. The Ni nanopowder included magnetic-ordered phases. The LGC synthesis yielded spherical particles with large coercivity while the abnormal initial magnetization curve for Ni indicated a non-collinear magnetic structure between the core and surface layer of the particles. Since the XRD pattern cannot actually distinguish between magnetite ($Fe_3O_4$) and maghemite (${\gamma}-Fe_2O_3$) as they have a spinel type structure, the phase of the iron oxide in the samples was unveiled by $M{\ddot{o}}ssbauer$ spectroscopy. The synthesized Ni-ferrite consisted of single domain particles, including an unusual ionic state. The synthesized nanopowder bore an active surface due to the defects that affected abnormal magnetic properties.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2003년도 하계학술연구발표회 및 한.일 공동심포지엄
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• pp.194-194
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• 2003

As a result of the recent miniaturization an enhancement in the performance of thin film inductors and thin film transformers, there are increased demands for the thin films with high magnetic permeability in the high frequency range, high saturation magnetization, in high electrical resistivity, and low coercive force. In order to improve high frequency properties, we will investigate anisotropy field by shape and size of pattern. The Fe-Al-O thin films of 16mm and 1 $\mu\textrm{m}$ thickness were deposited on Si wafer, using RF magnetron reactive sputtering technique with the mixture of argon and oxygen gases. The fabricating conditions are obtained in the working partial pressure of 2mTorr, O$_2$ partial pressure of 5%, input power of 400W, and Al pellets on an Fe disk with purity of 99,9%. Magnetic properties of the continuous films as followed: the 4$\pi$M$\_$s/ of 19.4kG, H$\_$c/ of 0.6Oe, H$\_$k/ of 6.0Oe and effective permeability of 2500 up to 100㎒ were obtained. In this work, we expect to enhance effect of magnetic anisotropy on patterned of Fe-Al-O thin films.

• 한국초전도ㆍ저온공학회논문지
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• 제25권4호
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• pp.50-53
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• 2023

In this study, the photolithography process was chosen to reduce the aspect ratio of the cross-section of a high-temperature superconducting (HTS) tape by dividing the superconducting layer of the tape. Reducing the aspect ratio decreases the magnetization losses in the second-generation HTS tapes generated by AC magnetic fields. The HTS tape used in the experiment has a thin silver (Ag) layer of about 2 ㎛ on top of the REBCO superconducting layer and no additional stabilizer layer. A dry film resist (DFR) was laminated on top of the HTS tape by a lamination method for the segmentation. Exposure to a 395 nm UV lamp on a patterned mask cures the DFR. Dipping with a 1% Na₂CO₃ solution was followed to develop the uncured film side and to obtain the required pattern. The silver and superconducting layers of the REBCO films were cleaned with an acid solution after the etching. Finally, the segmented HTS tape was completed by stripping the DFR film with acetone.

• 한국자기학회지
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• 제3권3호
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• pp.179-184
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• 1993

비정질 합금 $Fe_{78}Si_{9}B_{13}$의 구조를 X-선 회절상을 분석하여 구하였다. 계산된 동경분포함수(RDF)의 첫번째 peak는 최인접 원자의 분포를 나타내는 것으로 Gaussian 함수형태를 나타낸다. 구조분석에서 본 시료의 최인접 원자배위수는 13.5이고, 최인접 원자간 평균거리 $r_{0}$는 $2.595{\AA}$, 인접원자들의 분포를 나타내는 Gaussian 함수의 변수 ${\delta}r$은 $0.27{\AA}$이다. 저온에서의 포화자화의 온도 의존성은 spin 파로 설명할 수 있으며, 이 때에 계산된 spin파 stiffness 상수는 $117.8\;meV\;{\AA}^2$ 이다. 또한, 포화자화의 온도 의존성을 Handrich의 분자장 이론식과 맞추어 얻은 변수는 각각 S=1/2 일때 ${\Delta}=0.32$이고, S=1 일때 ${\Delta}=0.23$으로 이론식과 실험결과가 전체적으로 잘 일치한다. 구조분석 결과와 분자장 이론식에서 구한 변수를 활용하여 spin파 stiffness 상수를 계산할 수 있으며, 이로써 구한 값은 S=1/2일때 $149\;meV\;{\AA}^2$ 이고, S=1 일 때 $138\;meV\;{\AA}^2$ 이다. 또한, 평균 교환결합상수 J($r_{0}$)는 S=1/2일때 17.9 meV이고, S=1일때는 J($r_{0}$)는 6.7 meV 으로 추정된다.

• 한국의학물리학회지:의학물리
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• 제13권4호
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• pp.224-228
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• 2002

MR영상에 Spatial Modulation of Magnetization (SPAMM)과 같은 lagging 기법을 이용하여 심근의 움직임을 분석하여 임상에 적용하려는 많은 노력들이 이루어지고 있다. Tagging 대조도는 자동 tagline 검출 알고리즘을 사용하는 경우, 그 정확도에 영향을 미칠 수 있으며, 이는 tagline들 간의 간격에 의해 영향을 받을 수 있다. 본 연구의 목적은 SPAMM 영상에서 tagline 간격과 tagging 대조도와의 관계를 생체내 연구를 통해 알아보고자 하였다. 두 명의 건강한 지원자를 대상으로 1.5T MR 시스템에서 SPAMM 기반의 ECG triggered MR 영상을 획득하였다. 영상을 획득할 때, 먼저 3.6 mm에서 9.6 mm 사이의 간격을 가지는 수평 tagging stripe pattern의 tagline을 가하였다. 심실의 영상은 심장주기가 진행되는 동안 field echo EPI (FE-EPI) 기법을 이용하여 심실 중간 부분에서 얻었다 각 영상에 대한 tagging contrast-to-noise ratio (CNR)는 IDL을 이용한 프로그램을 사용하여 측정하였다. 분석 결과는, 심근의 수축이 진행되는 동안, tagline 간격이 좁은 경우 CNR은 급격한 감소를 나타내었으나, 간격이 넓은 경우에서는 CNR 감소 현상이 보이지 않았다. 같은 심장 위상에서, CNR은 tagline 간격이 넓어짐에 따라 증가하는 경향을 보였다. 특히, 완전히 수축한 심장 위상에서는, CNR의 변화가 다른 위상일 때와 비교해서 그 증가율이 높음을 알 수 있었다. 이러한 양상은 움직임이 없는 다른 주변 조직에서는 관찰되지 않았다. 결론적으로, 본 연구에서는 lagging 대조도가 tagline 간격 및 심근의 수축에 영향을 받을 수 있음을 알 수 있었으며, 앞으로 정확한 심근 움직임 연구를 위한 기초 자료로 쓰여질 수 있을 것이라 생각된다.