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11B NMR Study of the Spin Structures and the Dynamics in GdB4 Single Crystals
이무희,S. K. Nam,B. J. Mean,S. K. Kwon,S. H. Choi,B. K. Cho 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.4
11B nuclear magnetic resonance (NMR) measurements were performed on a single crystal of GdB4 to investigate the 4f spin structure and dynamics. The 11B NMR spectrum, shift, linewidth, spinlattice and spin-spin relaxation rates were measured down to 5 K at a field of 8 T perpendicular to the c-axis. Above TN = 42 K, the 11B NMR shift and linewidth were large due to the 4f moments of Gd. In addition, both were strongly temperature-dependent and proportional to the magnetic susceptibility. These facts confirm that the hyperfine field at the boron site originates from the 4f spins of Gd. Below TN, the single broad resonance peak of the 11B NMR split into various peaks, conrming that internal magnetic fields set in due to an antiferromagnetic phase transition. Assuming that the 4f spins of Gd are aligned antiferromagnetically and noncollinearly along the <110> direction in the basal plane perpendicular to the c-axis, we calculated the dipolar fields at the 16 boron nuclear sites from the 4f spins of Gd. The results show that the various peaks of the 11B NMR spectrum at 5 K are generally consistent with the calculation, suggesting that the noncollinear spin structure is a correct spin configuration. The relaxation rates, 1/T1 and 1/T2, were independent of temperature for temperatures above TN and then decreased tremendously. The vast variation of the relaxation rates indicates a rapid spin fluctuation at temperatures above TN and a huge suppression of the 4f spin fluctuation after the phase transition at TN.
11B NMR study of MgB2 superconductor
이무희,W.P. Halperin,조병기,이용일 한국자기공명학회 2005 Journal of the Korean Magnetic Resonance Society Vol.9 No.1
11B nuclear magnetic resonance (NMR) measurements have been performed to investigate electronic structures and vortex states of MgB2 superconductor. The central transition shows a narrow peak down to 25 K at 3.15 T. Below 25 K, an extra line starts to show up and dominates. The extra line is broad and asymmetric with a long tail in the high frequency side, which confirms that this originates from vortex pinning below the irreversibility temperature. From temperature evolution of the fraction and linewidth of the broad portion, temperature dependence of coherence length and penetration depth are extracted. 영어논문
중국경제의 생명코드가 해독과 중국경제의 이야기를 다각도로 외부에 전파
조로호,무희원 한국경영실무학회 2023 한국경영실무학회지 Vol.9 No.1
중국 공산당 제20차 전국대표대회 보고서는 완전한 미디어 커뮤니케이션 시스템의 구축을 강화 하고 새로운 주류 여론의 패턴을 형성할 것을 제안하였다. 미디어의 가치를 어떻게 발휘할 것인가, 중국 문화의 입장을 고수할 것인가, 중국 경제의 이야기를 어떻게 잘 전달할 것인가, 중국의 목소 리를 어떻게 확산시키고 세계무대에서 중국의 이미지를 형성할 것인가가 오늘날 주류 여론의 새로 운 발전 지표라고 할 수 있다. 본 연구는 중국 경제의 생명코드를 해독하는 것을 주요 주제로 삼 고, 중국 경제의 이야기가 해외에 전파될 수 있는 더 나은 소통의 길을 찾기 위해 좋은 이야기, 좋 은 언론인, 좋은 매체 등 여러 관점에서 중국 경제의 이야기를 잘 전달할 수 있는 방법을 논의하고자 하였다. The report of The 20th National Congress of the Communist Party of China proposes to strengthen the construction of a full media communication system and shape a new pattern of mainstream public opinion. How to bring into play the value of media, how to adhere to the position of Chinese culture, how to tell the story of China's economy well, how to spread China's voice and shape China's image on the world stage are the new development indicators of mainstream public opinion today. This study takes deciphering the life code of China's economy as the main narrative line, and discusses how to tell the story of China's economy well from multiple perspectives such as good stories, good journalists, and good media, in order to find a better communication path for the story of China's economy to be disseminated abroad.
Vortex Dynamics in Magnesium-diborides Superconductor using $^{11}$B NMR
규홍 이,무희 이 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.3
11B nuclear-magnetic-resonance (NMR) measurements were performed to investigate vortex dynamics in the polycrystalline superconductor MgB2. 11B NMR spectrum, shift and transverse relaxation rate 1=T2 were measured down to 4.3 K at 1.8 T. The spectrum below Tc exhibits a typical local eld distribution for a vortex lattice under a magnetic eld. The peak point of the spectrum shifts toward low magnetic eld, due to imperfect eld penetration. This decrease in the shift starts to appear below the detuning temperature of a NMR resonant circuit, which is measured to match the irreversibility temperature Tirr of magnetization. 1=T2 data, probing the slow motion of vortices, show a single peak with a small change in the rate, in contrast to the results for nickel borocarbides. This strongly suggests that thermal uctuation of vortices is reduced and the vortex motion is much smaller, compared with nickel borocarbides.
$^{11}$B NMR Study of Ferromagnetic CaB$_6$ Single Crystals
규홍 이,무희 이 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.1
11B nuclear-magnetic-resonance (NMR) measurements have been performed to microscopically investigate the electronic structure of the ferromagnetic state in three dierent compositions of calcium-hexaboride single crystals: Ca0:99B6, Ca0:995La0:005B6 and Ca0:99La0:01B6. Although three NMR lines are expected for the nuclear spin 3/2 of 11B, since the crystal structure of CaB6 is cubic and so all boron sites are equivalent, a larger number of NMR resonances have been observed. The frequency and intensity of these peaks distinctively change, depending on the angle between crystal axis and magnetic eld. Analyzing this behavior, we nd that the electric-eld gradient (EFG) tensor at the boron site has its principal axis perpendicular to the six cubic faces, with a quadrupole resonance frequency Q 600 kHz. Even though the magnetization data highlight the ferromagnetic hysteresis, 11B NMR shift and linewidth data show no clear microscopic evidence of the ferromagnetic state in three dierent compositions of CaB6 single crystals.