• 한국분말재료학회지
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• 제19권2호
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• pp.146-150
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• 2012

The effects of nano $Fe_xC$ addition to superconducting properties of $in$ $situ$ processed $MgB_2$ superconductors was examined. 0.1 wt.% and 1 wt.% nano $Fe_xC$ powders were mixed with boron and magnesium powders by ball milling. The powder mixtures were made into pellets by uniaxial pressing. The pellets were heat-treated at $700^{\circ}C-900^{\circ}C$ in argon atmosphere for $MgB_2$ formation. It was found by powder X-ray diffraction that the raw powders were completely converted into $MgB_2$ after the heat treatment. The superconducting transition temperature ($T_c$) and critical current density ($J_c$), estimated from susceptibility-temperature and $M-H$ curves, were decreased by nano $Fe_xC$ addition. The $T_c$ and $J_c$ decrease by nano $Fe_xC$ addition are attributed to the incorporation of iron and carbon with $MgB_2$ lattices (Fe substitution for Mg and C substitution for B) due to the high reactivity of the nano $Fe_xC$ powder.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.171-171
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• 2011

Co and Fe doped multi-wall carbon nano-tubes (MWCNTs) synthesized by microwave plasma enhanced chemical vapor deposition (PECVD) technique are investigated with synchrotron radiations at Pohang Light Source (PAL) and European Synchrotron Radiation Facility (ESRF). Near edge x-ray absorption spectroscopy (NEXAFS) measurement at C K, Co $L_{3,2}$ and Fe $L_{3,2}$-edges, and x-ray magnetic circular dichroism (XMCD) at Co and Fe $L_{3,2}$-edges have been carried at 7B1 XAS KIST and 2A MS beamline, respectively, to understand the electronic structure and responsible magnetic interactions at room temperature. X-ray absorption spectroscopy (XAS) at C K-edge shows significant p-bonding and Co and Fe L-edges proves the presence of $Co^{2+}$ and $Fe^{2+}$ in octahedral symmetry. Co and Fe doped MWCNTs show good XMCD spectra at 300K. The effect on the magnetism is also studied through swift heavy ion (SHI) radiations and magnetism is found enhanced and change in the electronic structure in Co-CNTs is investigated.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 초전도 자성체
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• pp.3-6
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• 2002

Effect of Ag additive element on microstructure of $Fe_{87-x}Zr_7B_6Ag_x$, magnetic thin films on Si(001) substrates has been investigated using Transmission Electron Microscopy(TEM) and X-ray Diffraction(XRD). All samples with additive Ag element were made by DC-sputtering and subjected to annealing treatments of $300^{\circ}C{\siim}600^{\circ}C$ for 1 hr. TEM and XRD showed that perfectly amorphous state in Ag-free Fe-based films was observed in as-deposited condition. The as-deposited Fe-based films with the presence of Ag constituent have a mixture of Fe-based amorphous and nano-sized Ag crystalline phases. In this case, additive element, Ag was soluted into Fe-based matrix. With the increase in additive element, Ag, insoluble nano-crystalline Ag particles were dispersed in the Fe-based amorphous matrix. Crystallization of Fe-based amorphous phase in the matrix of $Fe_{82}Zr_7B_6Ag_5$ thin films occurred at an annealing temperature of $400^{\circ}C$. Upon annealing, the amorphous-Ag crystalline state of Fe-Zr-B-Ag films was transformed into the mixture of Ag crystalline phase + Fe-based amorphous phase + ${\alpha}$-Fe cluster followed by the crystallization process of ${\alpha}$-Fe nanocrystalline + Ag crystalline phases.

• 한국세라믹학회지
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• 제45권6호
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• pp.320-323
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• 2008

The preparation of $Zn_xMn_{1-x}Fe_2O_4$ nanoparticles in an Igepal CO-520-cyclohexane water reverse micelle solution has been studied. The transmission electron microscopy and X-ray diffraction pattern analyses revealed the resulting particles to be $Zn_xMn_{1-x}Fe_2O_4$. The average size and distribution of the synthesized particles calcined at $500^{\circ}C$ for 5 h were in the range of 10 to 20 nm and broad, respectively. The phase of the synthesized particles was crystalline, the magnetic behavior of the synthesized particles was ferromagnetic. The effect of the synthesis parameters, such as the molar ratio of water to surfactant and calcination temperature, is discussed.

• 한국재료학회지
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• 제18권6호
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• pp.298-301
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• 2008

A preparation of $Ni_xMn_{1-x}Fe_2O_4$ nanoparticles produced via the reduction of Nickel nitrate hexahydrate, Manganese (II) nitrate hexahydrate and Iron nitrate nonahydrate with hydrazine in Igepal CO-520/cyclohexane reverse micelle solutions was investigated. Transmission Electron Microscope (TEM), X-ray Diffraction (XRD) and Vibration Sample Magnetometer (VSM) analyses showed that the resultant nanoparticles increased the molar ration of water to Igepal CO-520 as the concentrations of Nickel nitrate hexahyrate, Manganese (II) nitrate hexahydrate and Iron nitrate nonahydrate increased. The average size of the synthesized particles calcined at $600^{\circ}C$ for 2hrs was in the range of 20 nm to 30 nm, and the particle distribution was broadened. The phase of the synthesized particles was crystalline, and the magnetic behavior of the synthesized particles was superparamagnetism. The effect of the synthesis parameters of the molar ratio of water to surfactant and the calcination temperature was discussed.

• Journal of Magnetics
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• 제21권1호
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• pp.29-34
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• 2016

Nd-doped $BiFeO_3$ materials were synthesized via a sol-gel method. The crystal structure, magnetic properties, and complex impedance spectroscopy of multiferroic $Bi_{1-x}Nd_xFeO_3$ (BNFO) materials were investigated by X-ray diffraction (XRD), Raman scattering, vibrating sample magnetometer (VSM), and complex impedance spectroscopy. Our results show that the lattice crystal constants (a, c) and the ratio c/a of BNFO materials decreased with increasing Nd concentration. All samples exhibited weak ferromagnetism at room temperature, and the magnetization of samples was enhanced by the presence of $Nd^{3+}$ ions. There was an enhancement in the spontaneous magnetization of BFO with increasing Nd concentration, which is attributable to the collapse of the spin cycloid structure.

• 한국진공학회지
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• 제20권1호
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• pp.7-13
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• 2011

자기조립화된 Fe/Au 이중층 위에 $L1_0$형 구조를 갖는 FePd 나노 점을 성공적으로 제작하였다. AFM를 이용하여 초기에 편평한 Fe/Au 이중층 박막이 온도가 증가함에 따라서 응집되어 나노 점 구조로 변형되는 것을 확인하였다. 또한 형성된 이중층위에 FePd 다층막을 $300^{\circ}C$, $350^{\circ}C$, $400^{\circ}C$, $450^{\circ}C$에서 각각 증착하였다. 초격자 구조를 갖는 FePd 다층막의 표면형상은 응집현상에 의하여 자기조립화된 이중층의 형상과 유사하였다. XRD 측정결과, $350^{\circ}C$ 이상에서 열처리된 FePd 다층막은 $L1_0$형 구조를 갖는다는 것을 확인하였다. 그리고 박막두께에 따른 XPS 측정결과는 전체 박막의 화학적 조성이 증착순서와 일치하는 것을 보여주었다. 결과적으로 추가적인 식각공정 없이 화학적으로 규칙화된 FePd 초격자 나노 점의 제작에 성공하였다.

• 한국자기학회지
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• 제22권3호
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• pp.79-84
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• 2012

나노크기의 물질이 가지는 새로운 특성을 응용하는 연구가 매우 활발하게 진행되어 지고 있다. 본 연구에서는 PAD법으로 제조한 ${\alpha}$-Fe 나노분말을 이용하여 높은 포화자화와 기계적인 경도, 화학적 안정성, 작은 입자로 인한 tape noise의 감소 등의 특성을 지니고 있는 질화철인 $Fe_4N$을 합성하고, 이를 환원/확산법과 $N_2$가스 질화법으로 합성한 $Fe_{17}Sm_2N_x$ 자성분말과 자성 특성을 비교하였다. $NH_3+H_2$(부피비 3 : 1) 혼합가스를 이용하였을 경우 $Fe_4N$의 생성 온도와 반응시간 등의 조건 변수를 통해 $400^{\circ}C$에서 4시간 동안 열처리함으로서 단일상의 $Fe_4N$이 생성되는 것을 관찰 할 수 있었으며, 나노크기의 $Fe_4N$ 분말과 마이크론 크기의 $Fe_{17}Sm_2N_x$ 분말의 포화자화의 값은 각각 149, 117 emu/g의 값을 나타내었다.

• 한국분말재료학회지
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• 제11권6호
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• pp.486-492
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• 2004

We report the crystallization and magnetic properties of non-equilibrium $Al_{0.6}(Fe_{x}Cu_{1-x})_{0.4}(x=0.25, 0.50, 0.75)$ alloy powders produced by rod-milling as well as by new chemical leaching. X-ray diffractometry, transmission electron microscopy, differential scanning calorimetry and vibrating sample magnetometry were used to characterize the as-milled and leached specimens. After 400 h or 500 h milling, only the broad peaks of nano bcc crystalline phases were detected in the XRD patterns. The crystallite size, the peak and the crystallization temperatures increased with increasing Fe. After being annealed at $600{^\circ}C$ for 1 h for as-milled alloy powders, the peaks of bcc $AlCu_{4}\;and\;Al_{13}Cu_{4}Fe_{3}\;for\;x=0.25,\;bcc\;AlCu_{4}\;and\;Al_{5}Fe_{2}\;for\;x=0.50,\;and\;Al_{5}Fe_{2},\;and\;Al_{0.5}Fe_{0.5}\;for\;x=0.75$ are observed. After being annealed at $500{^\circ}\;and\;600{^\circ}C$for 1 h for leached specimens, these non-equi-librium phases transformed into fcc Cu and $CuFe_{2}O_{4}$phases for the x=0.25 specimen, and into bcc ${\alpha}-Fe,\;fcc\;Cu,\;and\;CuFe_{2}O_{4}$ phases for both the x=0.50 and the x=0.75 specimens. The saturation magnetization decreased with increasing milling time for $Al_{0.6}(Fe_{x}Cu_{1-x})_{0.4}$ alloy powders. On cooling the leached specimens from $800{\~}850^{\circ}C$,\;the magnetization first sharply increase at about $491.4{\circ}C,\;745{\circ}C,\;and\;750.0{\circ}C$ for x=0.25, x=0.50, and x=0.75 specimens, repectively.

• 한국재료학회지
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• 제20권3호
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• pp.137-141
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• 2010

The $(1-x)La_{0.7}Sr_{0.3}MnO_3(LSMO)/xZnFe_2O_4$(ZFO) (x = 0, 0.01, 0.03, 0.06 and 0.09) composites were prepared by a conventional solid-state reaction method. We investigated the structural properties, magnetic properties and electrical transport properties of (1-x)LSMO/xZFO composites using X-ray diffraction (XRD), scanning electron microscopy (SEM), field-cooled dc magnetization and magnetoresistance (MR) measurements. The XRD and SEM results indicate that LSMO and ZFO coexist in the composites and the ZFO mostly segregates at the grain boundaries of LSMO, which agreed well with the results of the magnetic measurements. The resistivity of the samples increased by the increase of the ZFO doping level. A clear metal-to-insulator (M-I) transition was observed at 360K in pure LSMO. The introduction of ZFO further downshifted the transition temperature (350K-160K) while the transition disappeared in the sample (x = 0.09) and it presented insulating/semiconducting behavior in the measured temperature range (100K to 400K). The MR was measured in the presence of the 10kOe field. Compared with pure LSMO, the enhancement of low-field magnetoresistance (LFMR) was observed in the composites. It was clearly observed that the magnetoresistance effect of x = 0.03 was enhanced at room temperature range. These phenomena can be explained using the double-exchange (DE) mechanism, the grain boundary effect and the intrinsic transport properties together.