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Kim, C.J.,Park, S.D.,Jun, B.H.,Kim, B.G.,Choo, K.N.,Ri, H.C. 한국초전도저온공학회 2014 한국초전도저온공학회논문지 Vol.16 No.1
Effects of neutron irradiation on the superconducting properties of the undoped $MgB_2$ and the carbon(C)-doped $MgB_2$ bulk superconductors, prepared by an in situ reaction process using Mg and B powder, were investigated. The prepared $MgB_2$ samples were neutron-irradiated at the neutron fluence of $10^{16}-10^{18}n/cm^2$ in a Hanaro nuclear reactor of KAERI involving both fast and thermal neutron. The magnetic moment-temperature (M-T) and magnetization-magnetic field (M-H) curves before/after irradiation were obtained using magnetic property measurement system (MPMS). The superconducting critical temperature ($T_c$) and transition width were estimated from the M-T curves and critical current density ($J_c$) was estimated from the M-H curves using a Bean's critical model. The $T_cs$ of the undoped $MgB_2$ and C-doped $MgB_2$ before irradiation were 36.9-37.0 K and 36.6-36.8 K, respectively. The $T_cs$ decreased to 33.2 K and 31.6 K, respectively after irradiation at neutron fluence of $7.16{\times}10^{17}n/cm^2$, and decreased to 22.6 K and 24.0 K, respectively, at $3.13{\times}10^{18}n/cm^2$. The $J_c$ cross-over was observed at the high magnetic field of 5.2 T for the undoped $MgB_2$ irradiated at $7.16{\times}10^{17}n/cm^2$. The $T_c$ and $J_c$ variation after the neutron irradiation at various neutron fluences were explained in terms of the defect formation in the superconducting matrix by neutron irradiation.
C.-J. Kim,S.-D. Park,B.-H. Jun,B. G. Kim,K.-N. Choo,H.-C. Ri 한국초전도저온공학회 2014 초전도와 저온공학 Vol.16 No.1
Effects of neutron irradiation on the superconducting properties of the undoped MgB2 and the carbon(C)-doped MgB2 bulk superconductors, prepared by an in situ reaction process using Mg and B powder, were investigated. The prepared MgB2 samples were neutron-irradiated at the neutron fluence of 1016-1018 n/cm2 in a Hanaro nuclear reactor of KAERI involving both fast and thermal neutron. The magnetic moment-temperature (M-T) and magnetization-magnetic field (M-H) curves before/after irradiation were obtained using magnetic property measurement system (MPMS). The superconducting critical temperature (Tc) and transition width were estimated from the M-T curves and critical current density (Jc) was estimated from the M-H curves using a Bean’s critical model. The Tcs of the undoped MgB2 and C-doped MgB2 before irradiation were 36.9-37.0 K and 36.6-36.8 K, respectively. The Tcs decreased to 33.2 K and 31.6 K, respectively after irradiation at neutron fluence of 7.16×1017 n/cm2, and decreased to 22.6 K and 24.0 K, respectively, at 3.13×1018 n/cm2. The Jc cross-over was observed at the high magnetic field of 5.2 T for the undoped MgB2 irradiated at 7.16×1017 n/cm2. The Tc and Jc variation after the neutron irradiation at various neutron fluences were explained in terms of the defect formation in the superconducting matrix by neutron irradiation.
Magnetic and Transport Properties of Ti0.96CoxNi0.04-xO2-δ Thin Films
J. H. Cho,Dong Ho Kim,D. H. Kim,E. C. Kim,H. C. Ri,T. J. Hwang,W. S. Yoon,Y. G. Joh 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.6
We investigated the magnetic and transport properties of Co and Ni co-doped TiO2 thin .lms grown by using a sol-gel method with Co and Ni concentrations from 0 % to 4 %. All the samples exhibited ferromagnetism at room temperature, but were highly resistive when annealed in vacuum at 650 ±C. The magnetic moment per ion increased with the Co concentration. After annealing at 850 ±C, the electrical conductance and the magnetic moment per ion of the .lms were enhanced, but a small Co metallic peak was observed in the X-ray diraction pattern. The Hall eect study showed that the carriers were electrons with densities lower than 1019 cm¡3 at room temperature for the samples annealed at 850 ±C. A weak anomalous Hall eect was observed and increased with the Co concentration. We discuss the co-doping eect by comparing the results with those of .lms singly doped with Ni or Co.
국가균형발전과 지방대학 육성 - 국립대학 육성 방안 -
이형철(H.-C. Ri) 한국지역사회학회 2021 지역사회연구 Vol.29 No.2
한국 고등교육은 1953년 한국전쟁 정전 이후 단시간에 세계에서 가장 가난했던 국가를 세계 경제 규모 10위의 선진국으로 진입시킨 발전 동력의 역할을 했다. 21세기 고도화된 지식기반 사회가 요구하는 인재 육성을 위해서는 고등교육 혁신의 필요성이 강조되고 있다. 한국 대학들은 2021년에 본격화된 학령인구 감소로 인한 대학미달사태와 국제경쟁력 추락 그리고 지방대학 몰락이라는 도전에 직면해있다. 본 연구는 국내 대학의 위기 타개를 위한 현실적이고 실현 가능한 방안으로 국립대학 육성정책을 제안한다. ‘국립대학법 제정과 국립대학 예산확충, 국립대학 무상교육, 그리고 국립대학의 자율성 보장’등과 같은 구체적인 정책 대안을 제시한다. Korea"s higher education served as the driving force for the development of the world"s poorest nation into the world"s 10th largest economy in a short period after the armistice of the Korean War in 1953. The need for innovation in higher education is being emphasized to foster human resources demanded by an advanced knowledge-based society in the 21st century. Korean universities face challenges of underachieving universities, falling international competitiveness, and the collapse of local universities due to a full-fledged decline in the school-age population in 2021. This study proposes a policy to foster national universities as a realistic and feasible way to tackle the crisis in Korean universities. Specific policy alternatives such as the enactment of the National University Act, the expansion of the budget for national universities, free education for national universities, and the guarantee of autonomy for national universities are proposed.
Structural and Magnetic Properties of Bimetallic FeCo Nanoclusters
이강호,S.H.Huh,J.W.Jeong,S.H.Kim,B.J.Choi,J.H.Jeong,이홍인,H-C.Ri 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.3
We produced bimetallic FexCo100_x nanoclusters (x = 0 ~ 100) with particle diameters of 5 30 nm by thermally decomposing two metal carbonyl vapors, Fe(CO)5 and Co2(CO)8, and we investigated their structural and magnetic properties as a function of x. The structural change with x was similar to that of the bulk alloy. However, we observed a superparamagnetism for 50 < x < 75 even though the bulk alloy is ferromagnetic for all x.
Magnetic Pinning Properties and Flux Jumps in Superconducting $MgB_2$
Yoon, W.S.,Lee, Eui-Wan,Kim, C.J.,Kim, B.G.,Ri, H.C. 한국초전도학회 2007 Progress in superconductivity Vol.9 No.1
Magnetization studies have been carried out on $MgB_2$ polycrystalline samples in the temperature range of 5 - 44 K and in the magnetic field up to 7 Tesla. The critical current density was calculated from hysteresis loops using the Bean's critical state model, and the highest value of $J_c$ at 20 K was $2.7{\times}10^5\;A/cm^2$ at 2 Tesla. The hysteresis loops were carefully examined to determine the temperature and magnetic field range where flux jumps appeared. The first jump occurred typically at 1 Tesla. Due to the strong pinning, we observed the presence of flux jump below H = 1 Tesla at temperature below 30 K.
Magneto-Photoluminescence and Spin Dynamics of Self-Assembled CdSe Quantum Dots in Zn1-xMnxSe
EunsoonOh,S.M.Soh,이중욱,K.J.Yee,J.C.Woo,H.S.Jeon,김대식,S.Lee,J.K.Furdyna,H.C.Ri,H.S.Chany,S.H.Park 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.6
We have studied photoluminescence spectra of CdSe self-assembled quantum dots (QD's) embedded in Zn$_{1-x}$Mn$_x$Se ($x$ = 0.05 and 0.15) with and without an external magnetic field. Under a magnetic field, the photoluminescence from CdSe QD's was circularly polarized under light excitation above the bandgap energy of ZnMnSe, indicating carrier spin polarization in CdSe QD's. The time-resolved photoluminescence study showed that spin-flip occured very rapidly as photocarriers transfered from the ZnMnSe to the CdSe QD's to reach statistical equilibrium of the spin states in the CdSe QD's. The Zeeman splitting in the CdSe QD's was several meV, still larger than the thermal energy at 5 K. These results suggest that the spin-polarization in CdSe QD's is mainly due to the Zeeman splitting of carriers in the CdSe quantum dots.
필라멘트 구조로 분리된 YBCO 박막에서 필라멘트 넓이와 간격이 교류손실에 미치는 영향
나동현,박현욱,김맹준,장용식,김지만,이형철,이용호,Na D. H,Park H. W,Kim M. J,Chang Y. S,Kim J. M,Ri H. C,Lee Y. H 한국초전도학회 2004 Progress in superconductivity Vol.6 No.1
To investigate the influence of strip width and inter-strip separation on the ac loss, arrays of parallel strips with different widths and separations were prepared. Studies on the hysteresis-loss characteristics of multifilamentary YBCO films were performed. The local magnetic field due to magnetization currents is measured by a scanning Hall probe microscope. Based on these results a conceptual design for a low loss YBCO coated conductor is suggested.