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NMR Study of Successive Magnetic Transitions in the A-site Ordered Perovskite LaMn3Cr4O12
Yu Kawasaki,Syota Takase,Yutaka Kishimoto,Takashi Ohno,Ikuya Yamada,Kentaro Shiro,Ryoji Takahashi,Kenya Ohgushi,Norimasa Nishiyama,Toru Inoue,Tetsuo Irifune 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We have investigated the successive magnetic phase transitions of the A-site ordered perovskiteLaMn3Cr4O12 by measuring 139La nuclear magnetic resonance (NMR) spectra. The successivemagnetic transitions are revealed by a very small but clear increase in the full width at half maximum(FWHM) of the 139La NMR signal at TM2 = 150 K and by the disappearance of the signal due to theline broadening at temperatures below TM1 = 50 K. These two magnetic transitions are associatedwith independent orderings within the Cr-site sublattice at TM2 and within the Mn-site sublatticeat TM1. Regarding the magnetic structure of the Cr-site sublattice at temperatures below TM2, thecancellation of internal fields at the La site, ruling out ferromagnetic and multi-q antiferromagneticstructures, is consistent with the typical antiferromagnetic structure for perovskites, such as G-,A- and C-type orders. The uncanceled internal field at the La site at temperatures below TM1is also consistent with these typical antiferromagnetic structures in the Mn-site sublattice. Thedifferences in the temperature dependences of the Knight shift K(T) and the bulk susceptibility χ(T) are consistently explained by the independent magnetic orderings of the Cr- and the Mn-sitesublattices and the cancellation of internal field originating from the Cr-site sublattice at the Lasite at temperatures below TM2.
51V-NMR Study of the Quasi-one-dimensional Antiferromagnet BaCo2V2O8
Yukiichi Ideta,Yu Kawasaki,Yutaka Kishimoto,Takashi Ohno,Yoshitaka Michihiro,Zhangzhen He,Yutaka Ueda,Mitsuru Itoh 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We have investigated the magnetic properties of quasi-one-dimensional antiferromagnetBaCo2V2O8 by the measurements of 51V-NMR spectrum. With decreasing temperature, Kk showsa broad peak around 30 K signaling the 1D short-range order in the Co2+ spin chain. The estimatedWeiss temperature Θ = −105 K, hyperfine coupling constants Akhf = 2.1 kOe/µB for H k c and Ahf= 2.6 kOe/µB for H ⊥ c at 13 kOe are comparable to those at 70.6 kOe. These results suggest thatstatic magnetic properties in the paramagnetic state are nearly independent of external magneticfield, although the ground N´eel state is suppressed by the application of external magnetic fieldabove Hc = 39 kOe along c-axis. In the antiferromagnetic state below TN = 5.4 K, the doublerectangle-like powder pattern was observed, indicating two V sites exposed to different size of internalfields, HA1 = 2.1 and HA2 = 3.8 kOe. The internal fields at V sites are explained by takinginto account of the classical and pseudo-dipolar fields from Co2+ magnetic moments.
전해 구리 도금된 활성탄소섬유에 의한 NO의 촉매 환원반응 메커니즘 연구
박수진,장유신,Kawasaki, Junjiro 한국화학공학회 2002 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.40 No.6
본 연구에서는 전해 도금되어진 활성탄소섬유(activated carbon fibers; ACFs)가 NO 환원거동에 미치는 영향에 대하여 고찰해보았다. 전해도금 시간이 증가함에 따라 탄소표면의 구리의 양은 점차 증가하였으나, 활성탄소섬유의 흡착 특성인 잘 발달된 비표면적 등의 기공구조는 약간씩 감소하는 경향을 보였다. 본 실험 결과, ACFs 및 ACFs/Cu 촉매 표면에서 500℃로 NO를 반응시켰을 때 NO가 N_2 및 O_2로 환원되는 것을 확인하였다. 특히, ACFs/Cu 촉매를 사용한 반응에서는 촉매반응 중 발생하는 산소를 촉매표면에서 잡아주는 역할을 하는 것으로 관찰되었다. 이는 NO환원에 있어서 ACFs와 ACFs/Cu 촉매 사이에 다른 기작이 있다는 것을 보여주는 것으로 생각되어진다. In this work, the catalytic reduction mechanisms of NO over ACFs/copper prepared by electrolytic copper plating has been studied. It was found that copper content on carbon surfaces increased with increasing the plating time. However, a slightly gradual decrease of adsorption properties, such as, BET specific surface area, was observed in increasing the plating times within the range of well-developed micropore structures. As experimental results, nitric oxide was converted into the nitrogen and oxygen on ACFs and ACFs/copper catalyst surfaces at 500℃. Especially, the surfaces of ACFs/copper catalyst were found to scavenge the oxygen released by catalytic reduction of NO, which could be explained by the presence of another nitric oxide reduction mechanism between ACFs and ACFs/copper catalysts.