Faculty Profiles - FURUKAWA Ko

Papers - FURUKAWA Ko

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Ferromagnetic Spin Coupling between Endohedral Metallofullerene La@C-82 and a Cyclodimeric Copper Porphyrin upon Inclusion Reviewed

Fatin Hajjaj, Kentaro Tashiro, Hidefumi Nikawa, Naomi Mizorogi, Takeshi Akasaka, Shigeru Nagase, Ko Furukawa, Tatsuhisa Kato, Takuzo Aida

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 133 ( 24 ) 9290 - 9292 2011.6

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

The cyclic host cyclo-[Pc-u](2) carrying two covalently connected Cu(II) porphyrin units can accommodate La@C-82, a paramagnetic endohedral metallofullerene, in its cavity to form the inclusion complex cyclo-[Pc-u](2)superset of La@C-82, which can be transformed into the caged complex cage-[Pc-u](2)superset of La@C-82 by ring-closing olefin metathesis of its side-chain olefinic terrnini. On the basis of electron spin resonance (ESR) and electron spin transient nutation (ESTN) studies, cyclo-[Pc-u](2)superset of La@C-82 is the first ferromagnetically coupled inclusion complex featuring La@C-82, whereas cage-[Pc-u](2)superset of La@C-82 is ferrimagnetic.

DOI： 10.1021/ja203491s

Structural investigation of the spin-singlet phase in (TMTTF)2I Reviewed

Ko Furukawa, Koichi Sugiura, Fumitatsu Iwase, Toshikazu Nakamura

Physical Review B - Condensed Matter and Materials Physics 83 ( 18 ) 2011.5

Language：English Publishing type：Research paper (scientific journal)

To elucidate the electronic state that exists in the boundary region between the spin-singlet phase and the high-pressure side antiferromagnetic phase in the modified generalized phase diagram, we carried out x-ray diffraction, electron spin resonance, and nuclear magnetic resonance measurements of the tetramethyl-tetrathia-fulvalene (TMTTF) family salt, (TMTTF)2I. The unit-cell volume of (TMTTF)2I is between that of (TMTTF)2Br and (TMTTF)2PF6. We found that (TMTTF)2I undergoes a spin-singlet phase transition at 21 K without involving paramagnetic charge-ordering phase. Therefore, the charge-ordering transition is not necessary for the spin-singlet transition of TMTTF salts as seen in other conventional spin-singlet salts. Finally, we discuss possible mechanisms of the spin-singlet phase transition. © 2011 American Physical Society.

DOI： 10.1103/PhysRevB.83.184419

Structural investigation of the spin-singlet phase in (TMTTF)(2)I Reviewed

Ko Furukawa, Koichi Sugiura, Fumitatsu Iwase, Toshikazu Nakamura

PHYSICAL REVIEW B 83 ( 18 ) 184419 2011.5

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

To elucidate the electronic state that exists in the boundary region between the spin-singlet phase and the high-pressure side antiferromagnetic phase in the modified generalized phase diagram, we carried out x-ray diffraction, electron spin resonance, and nuclear magnetic resonance measurements of the tetramethyl-tetrathiafulvalene (TMTTF) family salt, (TMTTF)(2)I. The unit-cell volume of (TMTTF)(2)I is between that of (TMTTF)(2)Br and (TMTTF)(2)PF6. We found that (TMTTF)(2)I undergoes a spin-singlet phase transition at 21 K without involving paramagnetic charge-ordering phase. Therefore, the charge-ordering transition is not necessary for the spin-singlet transition of TMTTF salts as seen in other conventional spin-singlet salts. Finally, we discuss possible mechanisms of the spin-singlet phase transition.

DOI： 10.1103/PhysRevB.83.184419

Photoinduced Triplet States of Photoconductive TTF Derivatives Including a Fluorescent Group Reviewed

Ko Furukawa, Yasuo Sugishima, Hideki Fujiwara, Toshikazu Nakamura

CHEMISTRY LETTERS 40 ( 3 ) 292 - 294 2011.3

Language：English Publishing type：Research paper (scientific journal) Publisher：CHEMICAL SOC JAPAN

The spin dynamics of photoconductive tetrathiafulvalene (TTF) derivatives containing 2,5-diphenyl-1,3,4-oxadiazole (PPD) was examined using time-resolved electron spin resonance (TR-ESR) spectroscopy. TR-ESR signals of a frozen solution sample under visible excitation were attributed to the excited triplet state T-1, which was populated via intersystem crossing from the excited singlet state S-1 as confirmed by TR-ESR spectral simulations. From DFT calculations, the spin-density distribution of the T-1 state was found to be concentrated around the linker between the TTF and PPD molecules.

DOI： 10.1246/cl.2011.292

Magnetic memory based on magnetic alignment of a paramagnetic ionic liquid near room temperature Reviewed

Yusuke Funasako, Tomoyuki Mochida, Takashi Inagaki, Takahiro Sakurai, Hitoshi Ohta, Ko Furukawa, Toshikazu Nakamura

CHEMICAL COMMUNICATIONS 47 ( 15 ) 4475 - 4477 2011

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

A paramagnetic ferrocenium-based ionic liquid that exhibits a magnetic memory effect coupled with a liquid-solid phase transformation has been developed. Based on field alignment of the magnetically anisotropic ferrocenium cation, the magnetic susceptibility in the solid state can be tuned by the weak magnetic fields (<1 T) of permanent magnets.

DOI： 10.1039/c0cc05820c

Novel Type of Career Generated System: Magnetic Investigations of TTF-Based Self-Doped Hydrogen-Bonding Conductor Reviewed

Ko Furukawa, Toshikazu Nakamura, Yuka Kobayashi, Takashi Ogura

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 ( 5 ) 053701 2010.5

Language：English Publishing type：Research paper (scientific journal) Publisher：PHYSICAL SOC JAPAN

Magnetic investigations, including static magnetic susceptibility and high-field electron spin resonance (ESR) measurements, were carried out for an organic conductor, (TTFCOO)[(NH4+1)(1-x)(NH3)(x)]. Anisotropic ESR parameters were determined for powder samples using a high-frequency W-band (93.9817 GHz) ESR spectrometer. The observed principal values of the g-tensor and quantum chemical calculation results indicate that the observed spin is distributed on quasi-hole-like TTF skeletons, and that the TTFCOO mainframe partially becomes a neutral radical. The temperature dependence of the spin susceptibility is well fitted with a Curie-Weiss term and an activation-type term, with the activation-type term dominant at high temperatures. The high absolute value of the spin susceptibility and the extremely small activation energy, Delta, indicate that a quasi-degenerate (metallic) state is stabilized in (TTFCOO)[(NH4+1)(1-x)(NH3)(x)], although the weakly temperature-dependent ESR linewidth indicates a localized characteristic. A novel type of carrier generation, self-doping, was discussed.

DOI： 10.1143/JPSJ.79.053701

Spin-Dynamics in Vicinity of Spin-Gap Phase Transition for Organic Conductor (TMTTF)(2)X Reviewed

Ko Furukawa, Toshifumi Hara, Toshikazu Nakamura

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 ( 4 ) 043702 2010.4

Language：English Publishing type：Research paper (scientific journal) Publisher：PHYSICAL SOC JAPAN

The spin dynamics in the vicinity of the spin-gap phase transition for the organic conductor (TMTTF)(2)PF6 were examined by pulsed-ESR spectroscopy. An anomaly in the relaxation time was observed in this intermediate region between the ground state and the high-temperature phase and was associated with the charge re-orientation originating in the transverse magnetic interaction. The calculation of the overlap integrals implied considerable inter-chain interactions. The transverse magnetic interaction plays an important role of the spin-gap phase transition in (TMTTF)(2)PF6.

DOI： 10.1143/JPSJ.79.043702

Submillimeter and millimeter wave ESR measurements of frustrated triangular lattice substance InMnO3 Reviewed

N. Matsumi, S. Okubo, M. Fujisawa, T. Sakurai, H. Ohta, K. Furukawa, T. Nakamura, H. Kikuchi

2009 34TH INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER, AND TERAHERTZ WAVES, VOLS 1 AND 2 574 - + 2009

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

Spin dynamics of S=2 triangluar lattice antiferromagnet have been investigated by the submillimeter and the millimeter wave ESR measurements of polycrystalline samples of InMnO3. Single absorption line is observed in whole temperature range from 2.0 K to 265 K. The resonance field shifts due to the development of internal field are observed below 40 K. The spin dynamics of InMnO3 will be discussed in connection with other triangluar lattice antiferromagnets.

The Molecular Solid from a Viewpoint of Photo-Induced Phase Transition and Related Phenomena

NAKAMURA Toshikazu, FURUKAWA Ko

rle 36 ( 6 ) 339 - 342 2008.6

Language：Japanese Publisher：The Laser Society of Japan

In this paper, we introduce the electronic states and electronic properties of molecular solid especially charge transfer salts and radical salts in the aspect of photo-induced phase transition and related phenomena. The characteristic features of molecular solid, which deeply related to photo-induced phase transition, are as following:(1) low-dimensional electronic states originated from anisotropic interaction,(2) strong electronic correlation induced by low carrier concentration,(3) lattice softness which causes competition of electronic phases with pressure and thermal contraction,(4) internal-freedom, namely, molecular motions. We propose strategies for exploring possible candidates for forthcoming materials with photo-induced phase transition.

DOI： 10.2184/lsj.36.339

Other Link： https://jlc.jst.go.jp/DN/JALC/00315542851?from=CiNii

Possible one-dimensional helical conductor: Hexa-peri-hexabenzocoronene nanotube Reviewed

Toshifumi Hara, Ko Furukawa, Toshikazu Nakamura, Yohei Yamamoto, Atsuko Kosaka, Wusong Jin, Takanori Fukushima, Takuzo Aida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 ( 3 ) 034710 2008.3

Language：English Publishing type：Research paper (scientific journal) Publisher：PHYSICAL SOC JAPAN

ESR and H-1 NMR investigations were performed on iodine-doped HBC nanotubes to understand the low-temperature electronic states and carrier dynamics. Using ESR measurements, we clarified that the charged carriers induced by iodine-doping possess spins, and we found two kinds of spin species with different doping levels. The ESR results indicate the itinerant features down to 170 K. The H-1 T-1(-1) for the heavy-iodine-doped HBC nanotubes follows T-0.5 and exhibits a characteristic frequency dependence. We propose that the spin excitation propagates along the one-dimensional helical chain.

DOI： 10.1143/JPSJ.77.034710

Redistribution of charge in the proximity of the spin-Peierls transition: C-13 NMR investigation of (TMTTF)(2)PF6 Reviewed

Toshikazu Nakamura, Ko Furukawa, Toshifumi Hara

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 ( 6 ) 064715 2007.6

Language：English Publishing type：Research paper (scientific journal) Publisher：PHYSICAL SOC JAPAN

C-13 nuclear magnetic resonance (NMR) investigations were carried out for a one-dimensional organic conductor, (TMTTF)(2)PF6, to determine the charge dynamics and configuration in the proximity of the spin-Peierls phase-transition temperature, T-sP. Although no obvious NMR line splitting associated with the charge-ordering transitions in the intermediate paramagnetic states was observed, the charge separation amplitude was estimated to be rho co similar to 0.14 using the C-13 NMR spin-lattice relaxation rates for the distinct lines. The abrupt decrease in the NMR linewidth below 25 K and the small anisotropy of the NMR linewidth in the spin-Peierls phase indicate the possible redistribution of the charge separation in the proximity of T-sP. The low-temperature electronic states of (TMTTF)(2)PF6 are discussed from a microscopic point of view.

DOI： 10.1143/JPSJ.76.064715

AF-like ground state of Mn-DNA and charge transfer from Fe to base-pi-band in Fe-DNA Reviewed

Kenji Mizoguchi, Shunsuke Tanaka, Masaya Ojima, Sayaka Sano, Mai Nagatori, Hirokazu Sakamoto, Yuki Yonezawa, Yuji Aoki, Hideyuki Sato, Kou Furukawa, Toshikazu Nakamura

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 ( 4 ) 043801 2007.4

Language：English Publishing type：Research paper (scientific journal) Publisher：PHYSICAL SOC JAPAN

The electronic states of M-DNA doped with M = Mg, Ca, Zn, Mn, Fe are investigated mainly with magnetic properties. In the "wet" condition the Mn ions of Mn-DNA form a 1-D chain in the center of a DNA double helix, as evidenced from the formation of the unnatural base pair combination with M, poly(dA)-M-poly(dC), but in the "dry" condition they form a 3-D network with the antiferromagnetic ground state around 0.4 K with the superexchange coupling via water molecules. The valence of 3+ is found only in Fe-DNA, from which the base pi-band obtains pi charge carriers.

DOI： 10.1143/JPSJ.76.043801

C-13 NMR analyses of successive charge ordering in (TMTTF)(2)ReO4 Reviewed

T Nakamura, K Furukawa, T Hara

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 ( 1 ) 13707 2006.1

Language：English Publishing type：Research paper (scientific journal) Publisher：PHYSICAL SOC JAPAN

C-13 NMR measurements were performed for a one-dimensional organic conductor, (TMTTF)(2)ReO4. The existence of an intermediate charge ordering (CO) phase was clarified for a TMTTF salt with a T-d symmetry counter anion by the C-13 NMR absorption line and spin-lattice relaxation rate, C-13 T-1(-1). The C-13 NMR spectra, which are characteristic of nuclei in equivalent molecules at room temperature, indicated two inequivalent molecules with unequal electron densities below 225 K. Moreover, the spin-singlet transition associated with ReO4 anion ordering was confirmed at around 158 K by C-13 NMR. The C-13 NMR lines show a marked change at 158 K. The possible redistribution of the electronic charge at the anion ordering temperature as well as the origin of the charge ordering phenomena are discussed.

DOI： 10.1143/JPSJ.75.013707

Ferromagnetic resonance studies on Ni80Fe20 wire arrays Reviewed

A. Maeda, M. Susaki, K. Furukawa, T. Takui

INTERMAG 2006 - IEEE International Magnetics Conference 934 2006

Deuteration effect and possible origin of the charge-ordering transition of (TMTTF)(2)X Reviewed

K Furukawa, T Hara, T Nakamura

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 ( 12 ) 3288 - 3294 2005.12

Language：English Publishing type：Research paper (scientific journal) Publisher：PHYSICAL SOC JAPAN

ESR, NMR and X-ray measurements were performed for pristine and fully perdeuterio-TMTTF, TMTTF-d(12) salts. Significant enhancement by deuteration of the charge-order phase transition temperature, Tco, was observed in ESR measurements for all (TMTTF)(2)X salts measured. No obvious relation between the SbF6 anion motion and the TMTTF charge-order was found by F-19 NMR. We also performed single crystal X-ray measurements to understand the deuteration effects and temperature dependence of the crystal structure. A possible relationship between the Tco's and crystallographical parameters is proposed. The deuteration effects and possible origin of the charge-ordering transition of TMTTF salts are discussed.

DOI： 10.1143/JPSJ.74.3288

The effect of deuteration on the transition into a charge ordered state of (TMTTF)(2)X salts Reviewed

F Nad, P Monceau, T Nakamura, K Furukawa

JOURNAL OF PHYSICS-CONDENSED MATTER 17 ( 41 ) L399 - L406 2005.10

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

From dielectric permittivity measurements, we show that deuteration yields a large increase of the transition temperature for the charge ordered state of (TMTTF)(2)X (X = AsF6, SbF6, ReO4) salts. We propose an explanation of this phenomenon, suggesting that deuteration induces a modification of the (TMTTF)(2)X crystal unit cell.

DOI： 10.1088/0953-8984/17/41/L01

High frequency EPR of the Mn-cluster in single crystals of cyanobacterial photosystem II Reviewed

Asako Kawamori, Jian-Ren Shen, Hiroyuki Mino, Ko Furukawa, Hideto Matsuoka, Tatsuhisa Kato

Photosynthesis: Fundamental Aspects to Global Perspectives 406 - 408 2005

Electrochemical polymerization of terthiophene-fullerene derivative and its optical property for organic solar cells Reviewed

M Morita, K Furukawa, Y Murata, T Yamazaki, K Komatsu, N Maruyama, T Yamao, S Fujita

2005 PACIFIC RIM CONFERENCE ON LASERS AND ELECTRO-OPTICS 516 - 517 2005

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

Poly(ethylenedioxy-substituted terthiophene -fullerene) was electrochemically synthesized on an ITO electrode, and its electronic and optical properties were measured. A large photocurrent of more than 3 mu A/cm(2) was observed by irradiation at 50 mW/cm(2) with a halogen lamp using a wet cell containing 5 mM methyl viologen.

Importance of fourth-order zero-field splitting terms in random-orientation EPR spectra of Eu(II)-doped strontium aluminate Reviewed

H Matsuoka, K Furukawa, K Sato, D Shiomi, Y Kojima, K Hirotsu, N Furuno, T Kato, T Takui

JOURNAL OF PHYSICAL CHEMISTRY A 107 ( 51 ) 11539 - 11546 2003.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

This work discusses an issue caused by omitting the fourth-order zero-field splitting (ZFS) terms in the analysis of random-orientation EPR spectra. Eu(II)-doped strontium aluminates were employed as a model system of the S-state lanthanoid ions, which have relatively large second-rank ZFS components, comparable to the conventional X-band microwave energy. The initial estimation of second- and fourth-rank ZFS components was acquired uniquely from the W-band spectrum based on a perturbation treatment of the spin Hamiltonian, and they were refined by a hybrid-eigenfield simulation approach. A parallel simulation of the X- and W-band spectra with the refined parameters reasonably reproduced both the observed spectra. The reliability of the parameters was also verified by reproducing the off-principal-axis extra lines arising from the M-S = 1/2 <----> 1/2 transition observed in the W-band spectrum. By comparison with an analysis based on the spin Hamiltonian omitting the fourth-order terms, it was concluded that omitting these terms results in an erroneous determination of the rhombic parameter (E) of the second-rank ZFS tensor. The obtained reliable second-rank ZFS tensors enabled us to invoke the superposition model, determining their principal-axis orientation. This is the first report of such relative orientation determined for Eu(II)-doped strontium aluminates.

DOI： 10.1021/jp030819

Pseudo-octahedral high-spin Co(II) complexes with orbitally degenerate ground states as studied by SQUID and ESR spectroscopy

H Matsuoka, T Yoshida, K Kubono, K Sato, D Shiomi, K Furukawa, T Kato, K Yokoi, T Takui

SYNTHETIC METALS 137 ( 1-3 ) 1213 - 1214 2003.4

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

High-spin Co(II) complexes (S = 3/2) with hydrogen bonding network were synthesized as models for magnetic quantum wires or 2D magnetic network systems. Their magnetic properties were characterized in terms of the SQIUD measurement. An analysis for the magnetic susceptibilities assuming an effective angular momentum L'=1 reproduced the experimental temperature dependences of the susceptibilities. In order to evaluate intermolecular magnetic interactions, it turned out that models beyond Heisenberg-Dirac exchange Hamiltonian are required for the analysis.

DOI： 10.1016/S0379-6779(02)01047-0

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