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Tb이 치환된 $RuSr_2(Eu_{1.34}Ce_{0.66})Cu_2O_z$ 계의 초전도 및 자기적 특성
이호근,이만석,Lee, H.K.,Lee, M.S. 한국초전도학회 2012 Progress in superconductivity Vol.14 No.2
Samples with nominal compositions of $RuSr_2(Eu_{1.34-x}Tb_xCe_{0.66})Cu_2O_z$ (x = 0, 0.67) were prepared and their superconductivity and magnetic properties were compared to shed light on the effect of Tb substitution for Eu. X-ray diffraction measurements indicate that the Tb substitution resulted in a decrease in both a and c lattice parameters in consistent with ionic size difference between Eu and Tb. Contrary to the Tb-free sample, no superconducting transition behavior is observed in the Tb-sustituted sample. It is also found that the Tb substitution for Eu significantly increases the weak-ferromagnetic component of the field-cooled magnetic susceptibility as well as an increase in the magnetic ordering temperature. These results suggest that the magnetic state of the Ru sublattice is significantly affected by the Tb substitution for Eu.
RF 마그네트론 스퍼터링 방법으로 제작된 질화탄소 박막의 광학적 특성
이호근,김영호,정기룡 한국물리학회 2004 새물리 Vol.49 No.5
The effects of the film growth temperature, T$_s$ on the optical properties, the chemical bond structure and the microstructure of carbon-nitride (CN$_x$) thin films deposited by using RF magnetron sputtering in a pure N$_2$ discharge are reported. For a given N$_2$ pressure of 150 mTorr, the deposition rate R$_d$, the N/C ratio, and the optical band gap, E$_g$, decrease with increasing T$_s$ from 40 $^\circ$C to 350 $^\circ$C. Analyses of X-ray photoelectron spectroscopy spectra show that the hybridized sp$^3$C-N bonding fraction increases with increasing T$_s$. The surface of the films grown at high T$_s$ tend to be relatively smooth and homogeneous compared to the surface of the films grown at room temperature without substrate heating. 본 연구에서는 RF 마그네트론 스퍼터링 방법으로 순수 질소가스 분위기에서 제작된 질화탄소 박막에 대해 증착온도가 광학적 특성, 화학적 결합 특성 및 마이크로 표면구조 특성에 미치는 효과를 연구했다. 150 mtorr 의 N$_2$ 압력 하에서 제작된 질화탄소 박막은 증착온도가 40 $^\circ$C 에서 350 $^\circ$C 범위로 증가될 때 증착율, N/C 조성비 및 광학적 E$_{g}$ 값 모두 감소했다. XPS 스펙트럼 분석결과는 증착온도가 증가될 경우 sp$^{3}$C-N 결합성분이 증가되는 특성을 보여 주었다. 증착시 기판의 온도가 높을 수록 기판을 가열하지 않고 제작된 시편에 비해 표면구조가 상대적으로 조밀해지고 균질해짐을 알 수 있었다.
Performance Evaluation of a Quarter-vehicle MR Suspension System with Different Tire Pressure
이호근,성금길,최승복,박민규,박명규 한국정밀공학회 2011 International Journal of Precision Engineering and Vol. No.
This paper evaluates performance of a quarter-vehicle magneto-rheological (MR) suspension system with respect to different tire pressure. In order to achieve this goal, controllable MR damper that satisfies design specifications for a midsized commercial passenger vehicle is designed and manufactured based on the optimized damping force levels and mechanical dimensions. After experimentally evaluating the field-dependent characteristics of the manufactured MR damper, the quarter-vehicle suspension system consisting of sprung mass, spring, tire and the MR damper is constructed in order to investigate the ride comfort. After deriving the equations of the motion for the proposed quarter-vehicle MR suspension system, vertical tire stiffness with respect to different tire pressure is experimentally identified. The skyhook controller is then implemented for the realization of quarter-vehicle MR suspension system. Ride comfort characteristics such as vertical acceleration RMS (root mean square) and WRMS (weighted RMS) of sprung mass are evaluated under bump and random road conditions using a quarter-vehicle test facility.
Cu 치환에 따른 $(Ru_{1-x}Cu_x)Sr_2(Eu_{1.34}Ce_{0.66})Cu_2O_z$ 계의 초전도 특성
이호근,Lee, H.K. 한국초전도학회 2009 Progress in superconductivity Vol.11 No.1
The effect of Cu substitution on the structural and superconducting properties of the $(Ru_{1-x}Cu_x)Sr_2(Eu_{1.34{\cdot}}Ce_{0.66})Cu_2O_z$ system with x = 0, 0.25 and 0.5 prepared under ambient pressure have been investigated. The X-ray diffraction patterns indicated that the Ru ions are replaced by the Cu ions. It is found that the Cu substitution for Ru significantly reduces the ferromagnetic component of field-cooled magnetic susceptibility, but results in a small change in diamagnetic onset transition temperature of zero-field-cooled magnetic susceptibility. In contrast to the Ru $Sr_2(Eu_{1.34{\cdot}}Ce_{0.66})Cu_2O_z$, bulk Meissner effect is observed in the field-cooled magnetization measurements of the Cu doped samples. The experimental results are discussed in connection with the spontaneous vortex phase interpretation.
Nb 및 Tb치환에 따른 (Ru{1-y}Nb{y})Sr{2}(Nd{0.67}Tb{0.67}Ce{0.66})Cu{2}O{z} 계의 구조 및 자기적 특성
이호근,김가원 한국물리학회 2014 새물리 Vol.64 No.10
Polycrystalline samples of (Ru{0.9}Nb{0.1})Sr{2}(Nd {1-x/2}Tb{1-x/2}Ce{x})Cu{2}O{z} (0.5 ≤ x ≤ 1.0) and (Ru{1-y}Nb{y})Sr{2}(Nd{0.67}Tb{0.67}Ce{0.66})Cu{2}O{z} (0 ≤ y ≤ 1.0) were synthesized by using a solid-state reaction method. The structure and the magnetic properties were investigated by means of X-ray diffraction (XRD) and magnetization measurements. XRD data revealed that almost single-phase samples could be obtained for x = 0.66 - 0.8. Nb substitution was also found to result in a reduction of the weak-ferromagnetic component of the field-cooled (FC) magnetization and a reduction in the magnetic-ordering temperature. Based on the results of a Rietveld refinement of the XRD data, we discuss the structure and the magnetic behaviors induced by Nb doping and the local structural changes in the Ru sublattice. (Ru{0.9}Nb{0.1})Sr{2}(Nd{1-x/2}Tb{1-x/2}Ce{x})Cu{2}O{z} (0.5 ≤ x ≤ 1.0)과 (Ru{1-y}Nb{y})Sr{2}(Nd{0.67}Tb{0.67} Ce{0.66})Cu{2}O{z} (0 ≤ y ≤ 1.0) 조성의 다결정 시편을 고상 반응법으로 합성하고 그 구조와 자기적 특성을 X-선 회절 (XRD) 및 자화도 특성 측정을 통해 연구했다. XRD 분석 결과는 x = 0.66 - 0.8 일 때 거의 단일상 시편이 합성됨을 보여 주었다. 또한 Nb의 치환량이 증가되면 자기전이 온도 뿐 아니라 field-cooled (FC) 측정법으로 측정된 약한 강자성 성분의 크기도 감소됨이 관측되었다. Nb 치환으로 야기된 구조 및 자기적 특성를 XRD 데이터의 Rietveld 분석으로 얻어진 Ru 주위의 국소구조 변화와 연계하여 논의되었다.