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Genta Kawaguchi Prof. Dr. Mitsuhiko Maesato Dr. Tokutaro Komatsu Prof. Dr. Hiroshi Kitagawa Prof. Dr. Tatsuro Imakubo Dr. Andhika Kiswandhi Dr. David Graf Prof. Dr. James S. Brooks 《Angewandte Chemie (International ed. in English)》2015,54(35):10169-10172
Simultaneous manipulation of both spin and charge is a crucial issue in magnetic conductors. We report on a strong correlation between magnetism and conductivity in the iodine‐bonded molecular conductor (DIETSe)2FeBr2Cl2 [DIETSe=diiodo(ethylenedithio)tetraselenafulvalene], which is the first molecular conductor showing a large hysteresis in both magnetic moment and magnetoresistance associated with a spin‐flop transition. Utilizing a mixed‐anion approach and iodine bonding interactions, we tailored a molecular conductor with random exchange interactions exhibiting unforeseen physical properties. 相似文献
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Peter Niedbalski Christopher Parish Andhika Kiswandhi Lloyd Lumata 《Magnetic resonance in chemistry : MRC》2016,54(12):962-967
The nitroxide‐based free radical 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) is a widely used polarizing agent in NMR signal amplification via dissolution dynamic nuclear polarization (DNP). In this study, we have thoroughly investigated the effects of 15N and/or 2H isotopic labeling of 4‐oxo‐TEMPO free radical on 13C DNP of 3 M [1‐13C] sodium acetate samples in 1 : 1 v/v glycerol : water at 3.35 T and 1.2 K. Four variants of this free radical were used for 13C DNP: 4‐oxo‐TEMPO, 4‐oxo‐TEMPO‐15N, 4‐oxo‐TEMPO‐d16 and 4‐oxo‐TEMPO‐15N,d16. Our results indicate that, despite the striking differences seen in the electron spin resonance (ESR) spectral features, the 13C DNP efficiency of these 15N and/or 2H‐enriched 4‐oxo‐TEMPO free radicals are relatively the same compared with 13C DNP performance of the regular 4‐oxo‐TEMPO. Furthermore, when fully deuterated glassing solvents were used, the 13C DNP signals of these samples all doubled in the same manner, and the 13C polarization buildup was faster by a factor of 2 for all samples. The data here suggest that the hyperfine coupling contributions of these isotopically enriched 4‐oxo‐TEMPO free radicals have negligible effects on the 13C DNP efficiency at 3.35 T and 1.2 K. These results are discussed in light of the spin temperature model of DNP. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Kismarahardja A Brooks JS Kiswandhi A Matsubayashi K Yamanaka R Uwatoko Y Whalen J Siegrist T Zhou HD 《Physical review letters》2011,106(5):056602
Studies of the structure, magnetization, and resistivity under pressure on stoichiometric normal spinel Co[V(2)]O(4) single crystals show (i) absence of a structural distortion, (ii) abnormal magnetic critical exponents, and (iii) metallic conductivity induced by pressures at low temperatures. All these results prove that Co[V(2)]O(4) sits on the edge of the itinerant-electron limit. Compared with similar measurements on Fe[V(2)]O(4) and other A[V(2)]O(4) studies, it is shown that a critical V-V separation for a localized-itinerant electronic phase transition exists. 相似文献
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Peter?Niedbalski Christopher?Parish Qing?Wang Andhika?Kiswandhi Lloyd?LumataEmail authorView authors OrcID profile 《Applied magnetic resonance》2017,48(9):933-942
The nitroxide-based 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) free radical is widely used in 13C dynamic nuclear polarization (DNP) due to its relatively low cost, commercial availability, and effectiveness as polarizing agent. While a large number of TEMPO derivatives are available commercially, so far, only few have been tested for use in 13C DNP. In this study, we have tested and evaluated the 13C hyperpolarization efficiency of eight derivatives of TEMPO free radical with different side arms in the 4-position. In general, these TEMPO derivatives were found to have slight variations in efficiency as polarizing agents for DNP of 3 M [1-13C] acetate in 1:1 v/v ethanol:water at 3.35 T and 1.2 K. X-band electron paramagnetic resonance (EPR) spectroscopy revealed no significant differences in the spectral features among these TEMPO derivatives. 2H enrichment of the ethanol:water glassing matrix resulted in further improvement of the solid-state 13C DNP signals by factor of 2 to 2.5-fold with respect to the 13C DNP signal of non-deuterated DNP samples. These results suggest an interaction between the nuclear Zeeman reservoirs and the electron dipolar system via the thermal mixing mechanism. 相似文献
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Keizo Murata Woun Kang Kosuke Masuda Tetsuji Kuse Takahiko Sasaki Keiichi Yokogawa Harukazu Yoshino James S. Brooks Eun Sang Choi Andhika Kiswandhi Reizo Kato 《Physica B: Condensed Matter》2012,407(11):1927-1929
Field-induced successive transitions were observed in magnetoresistance in the quasi-one-dimensional organic conductor, HMTSF-TCNQ, hexamethylene-tetraselena-fulvalene-tetracyanoquinodimethane. The magnetoresistance exhibits kink transitions accompanying hysteresis at pressures around 1 GPa, but neither at p=0 nor at 2 GPa. At p=0 and below 30 K, this material undergoes charge density wave (CDW) state, which is suppressed around 1 GPa, where successive transitions are observed. Since these behavior is only observed at the boundary in pressure between insulator and metal, and the nature of the insulating state is CDW at p=0, it is strongly suggested that the successive transitions observed in magnetoresistance might be associated with CDW, accordingly a field-induced CDW by the one-dimensionalization by strong magnetic field ranging from 10 to 30 T. The behaviors are compared with previously claimed FICDW and the established FISDW (field-induced-spin-density-wave). 相似文献
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Construction and 13C hyperpolarization efficiency of a 180 GHz dissolution dynamic nuclear polarization system 下载免费PDF全文
Andhika Kiswandhi Peter Niedbalski Christopher Parish Sarah Ferguson David Taylor George McDonald Lloyd Lumata 《Magnetic resonance in chemistry : MRC》2017,55(9):828-836
Dynamic nuclear polarization (DNP) via the dissolution method has become one of the rapidly emerging techniques to alleviate the low signal sensitivity in nuclear magnetic resonance (NMR) spectroscopy and imaging. In this paper, we report on the development and 13C hyperpolarization efficiency of a homebuilt DNP system operating at 6.423 T and 1.4 K. The DNP hyperpolarizer system was assembled on a wide‐bore superconducting magnet, equipped with a standard continuous‐flow cryostat, and a 180 GHz microwave source with 120 mW power output and wide 4 GHz frequency tuning range. At 6.423 T and 1.4 K, solid‐state 13C polarization P levels of 64% and 31% were achieved for 3 M [1‐13C] sodium acetate samples in 1 : 1 v/v glycerol:water glassing matrix doped with 15 mM trityl OX063 and 40 mM 4‐oxo‐TEMPO, respectively. Upon dissolution, which takes about 15 s to complete, liquid‐state 13C NMR signal enhancements as high as 240 000‐fold (P=21%) were recorded in a nearby high resolution 13C NMR spectrometer at 1 T and 297 K. Considering the relatively lower cost of our homebuilt DNP system and the relative simplicity of its design, the dissolution DNP setup reported here could be feasibly adapted for in vitro or in vivo hyperpolarized 13C NMR or magnetic resonance imaging at least in the pre‐clinical setting. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
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