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57Fe가 치환된 TiO₂의 결정학적 및 뫼스바우어 분광학적 연구
이희민(Hi Min Lee),심인보(In-Bo Shim),김철성(Chul Sung Kim) 한국자기학회 2003 韓國磁氣學會誌 Vol.13 No.6
Ti_(1-x)(57)^FeO₂(0.0≤x≤0.07) compounds were fabricated using the sol-gel method, and the crystal structure and magnetic properties were investigated as a function of doped (57)^Fe concentration. X-ray diffraction patterns showed a pure anatase single phase, without any segregation of Fe into particulate. With varying (57)^Fe concentration, we could observe unusual magnetic phenomena in these materials. Doping (57)^Fe into the TiO₂ nonmagnetic semiconductor formed magnetic properties, but the gradual increase of (57)^Fe concentration decreased rapidly the ferromagnetic properties rather than enhanced the ferromagnetic properties. Obvious ferromagnetic behavior was shown for the samples with x≤0.01, while paramagnetic behavior was shown for the sample with x≥0.03. These phenomena could be verified using Mossbauer measurement. Separation of the ferromagnetic phase (sextet) and the paramagnetic phase (doublet) of the samples with different (57)^Fe concentration was characterized. Samples with x≤0.01 have sextet and doublet simultaneously, but samples with x≥0.03 have only doublet at room temperature. This indicates that the sample x≤0.01 have the ferromagnetic phase at room temperature. This result corresponded with the M-H loops referenced above and reveals an interesting feature that there is a critical limit of 57Fe concentration (0.01<x<0.03) to get ferromagnetic properties at room temperature. Also, the observed small magnetic moment per Fe atom of x≤0.01 samples was fundamentally attributable to the paramagnetic phase as well as the ferromagnetic phase.
기판 효과에 따른 저 자장 영역에서의 자기저항 효과에 관한 연구
이희민(Hi Min Lee),심인보(In-Bo Shim),김철성(Chul Sung Kim) 한국자기학회 2002 韓國磁氣學會誌 Vol.12 No.2
The low-field tunnel-type magnetoresistance (MR) properties of sol-gel derived La_(0.7)Pb_(0.3)MnO₃ (LPMO) thin film deposited on different substrate have been investigated. Polycrystalline thin films were fabricated by spin-coating on SiO₂/Si(100) substrate and that with yttria-stabilized zirconia (YSZ) buffer layer, while c-axis-oriented thim film was grown on LaAlO₃(001) (LAO) single crystal substrate. The full width half maximum (FWHM) of the rocking curve scan of LPMO/LAO film is 0.32°. Tunnel-type MR ratio is 0.52 % in LPMO/SiO₂/Si(100) film and that of LPMO/YSZ/SiO₂/Si(100) film is as high as 0.68 %, whereas that of LPMO/LAO(001) film is less than 0.4 % under the applied field of 500 Oe at 300 K. Well-pronounced MR hysteresis was registered with an MR peak in the vicinity of the coercive field. The low-field tunnel-type MR characteristics of thin films deposited on different substrates originates from the behavior of grain boundary properties.
비스무스 나노분말 표지 전극의 카드뮴/납 검출특성에 관한 연구
이경자,김현진,이희민,이상훈,이민구,이창규,Lee, Gyeoung-Ja,Kim, Hyoun-Jin,Lee, Hi-Min,Lee, Sang-Hoon,Lee, Min-Ku,Lee, Chang-Kyu 한국분말야금학회 2008 한국분말재료학회지 (KPMI) Vol.15 No.5
Trace analysis of Cd and Pb at surface modified thick film graphite electrode with Bi nanopowder has been carried out using square-wave anodic stripping voltammetry (SWASV) technique. Bi nanopowder synthesized by gas condensation (GC) method showed the size of $50{\sim}100$ nm with BET surface area, $A_{BET}=6.8m^{2}g^{-l}$. For a strong adhesion of the Bi nanopowder onto the screen printed carbon paste electrode, nafion solution was added into Bi-containing suspension. From the SWASV, it was found that the Bi nanopowder electrode exhibited a well-defined responses relating to the oxidations of Cd and Pb. The current peak intensity increased with increasing concentration of Cd and Pb. From the linear relationship between Cd/Pb concentrations and peak current, the sensitivity of the Bi nanopowder electrode was quantitatively estimated. The detection limit of the electrode was estimated to be $0.15{\mu}g/l$ and $0.07{\mu}g/l$ for Cd and Pb, respectively, on the basis of the signal-to-noise characteristics (S/N=3) of the response for the $1.0{\mu}g/l$ solution under a 10 min accumulation.