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161 results on '"Suematsu, Hiroyoshi"'

1. Ferromagnetism and giant magnetoresistance in the rare earth fullerides Eu6-xSrxC60

Author

Ishii, Kenji, Fujiwara, Akihiko, Suematsu, Hiroyoshi, and Kubozono, Yoshihiro

Subjects
Condensed Matter - Materials Science
Abstract

We have studied crystal structure, magnetism and electric transport properties of a europium fulleride Eu6C60 and its Sr-substituted compounds, Eu6-xSrxC60. They have a bcc structure, which is an isostructure of other M6C60 (M represents an alkali atom or an alkaline earth atom). Magnetic measurements revealed that magnetic moment is ascribed to the divalent europium atom with S = 7/2 spin, and a ferromagnetic transition was observed at TC = 10 - 14 K. In Eu6C60, we also confirm the ferromagnetic transition by heat capacity measurement. The striking feature in Eu6-xSrxC60} is very large negative magnetoresistance at low temperature; the resistivity ratio \rho(H = 9 T)/\rho(H = 0 T) reaches almost 10^{-3} at 1 K in Eu6C60. Such large magnetoresistance is the manifestation of a strong pi-f interaction between conduction carriers on C60 and 4f electrons of Eu., Comment: 5 pages, 4 figures

Published
2002
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6. Magnetic structure of the europium fulleride ferromagnet Eu(sub 6)C(sub 60)

Author

Margiolaki, Irene, Margadonna, Serena, Prassides, Kosmas, Hansen, Thomas, Ishii, Kenji, and Suematsu, Hiroyoshi

Subjects
Europium -- Structure, Europium -- Magnetic properties, Neutrons -- Diffraction, Neutrons -- Observations, Chemistry
Abstract

The first magnetic structure determination of a fullerene-based molecular ferromagnet by powder neutron diffraction is provided. The lanthanide exchange interactions in Eu(sub 6)C(sub 60) are modulated by the C(sub 60) anions and orbital mixing can account for the observed magnetic and conducting properties of the material.

Published
2002

7. C_<70> Molecular Stumbling inside Single-Walled Carbon Nanotubes

Author

Maniwa, Yutaka, Kataura, Hiromichi, Abe, Masatoshi, Fujiwara, Akihiko, Fujiwara, Ryuji, Kira, Hiroshi, Tou, Hideki, Suzuki, Shinzo, Achiba, Yohji, Nishibori, Eiji, Takata, Masaki, Sakata, Makoto, and Suematsu, Hiroyoshi

Subjects
peapod, phase transition, XRD, fullerene, SWNT, structure, carbon nanotube, %22">C_<70>, thermal expansion
Abstract

We report the structural study of C_-one-dimensional (1D) crystal formed inside single-walled carbon nanotubes (SWNTs). X-ray diffraction measurements were performed between 100 K and 999 K on C_-encapsulated SWNTs with an average diameter of 1.37 nm. Two different domains, where the dominant alignment of C_ molecular long axis is standing or lying with respect to the tube axis, were observed; the ratio of the standing to the lying C_-domains is roughly 7:3. Thermal expansion of interfullerene distance gave no evidence for orientational phase transitions, not as in the 3D crystals. Instead, the long-range order of the standing C_-alignment was thermally destroyed with an activation energy of 39±4 meV. The results imply the importance of either the 1D fluctuation or the tube-C_ interaction at finite temperatures.

Published
2003

8. Structural phase transition in the ammoniated alkali C_<60> compound (NH_3)K_3C_<60>

Author

Ishii, Kenji, Watanuki, Tetsu, Fujiwara, Akihiko, Suematsu, Hiroyoshi, Iwasa, Yoshihiro, Shimoda, Hideo, Mitani, Tadaoki, Nakao, Hironori, Fujii, Yasuhiko, Murakami, Youichi, and Kawada, Hajime

Subjects
Condensed Matter::Superconductivity
Abstract

X-ray diffraction measurements of (NH_3)K_3C_60 have revealed a structural phase transition at T_s=150 K, which is attributed to the orientational order-disorder transition of the K-NH_3 pair at the octahedral site of the C_60 lattice. The low-temperature phase has a face-centered-orthorhombic structure derived by doubling the unit lattice vectors of the high-temperature phase along three axes. The superlattice intensity increases continuously below T_s, which means that the transition is second order. At 100 K

Published
1999

11. Thermal expansion of single-walled carbon nanotube (SWNT) bundles: X-ray diffraction studies

Author

Maniwa, Yutaka, Fujiwara, Ryuji, Kira, Hiroshi, Tou, Hideki, Kataura, Hiromichi, Suzuki, Shinzo, Achiba, Yohji, Nishibori, Eiji, Takata, Masaki, Sakata, Makoto, Fujiwara, Akihiko, Suematsu, Hiroyoshi, Maniwa, Yutaka, Fujiwara, Ryuji, Kira, Hiroshi, Tou, Hideki, Kataura, Hiromichi, Suzuki, Shinzo, Achiba, Yohji, Nishibori, Eiji, Takata, Masaki, Sakata, Makoto, Fujiwara, Akihiko, and Suematsu, Hiroyoshi

Abstract

type:text, Thermal expansion coefficient in single-walled carbon nanotube bundles was determined as (-0.15±0.20)×10-5 (1/K) for the tube diameter and (0.75±0.25)×10-5 (1/K) for the triangular lattice constant by means of x-ray scattering between 300 K to 950 K. The value for the intertube gap was (4.2±1.4)×10-5 (1/K), which is larger than 2.6×10-5 (1/K) for the c-axis thermal expansion in graphite. The results reveal the presence of a remarkably larger lattice anharmonicity in nanotube bundles than that of graphite. The small value for the tube diameter is consistent with the seamless tube structure formed by a strong covalent bond between carbon atoms comparable to that in graphite.

Published
2001

12. Photoconductivity in Semiconducting Single-Walled Carbon Nanotubes

Author

Fujiwara, Akihiko, Matsuoka, Yasuyuki, Suematsu, Hiroyoshi, Ogawa, Naoki, Miyano, Kenjiro, Kataura, Hiromichi, Maniwa, Yutaka, Suzuki, Shinzo, Achiba, Yohji, Fujiwara, Akihiko, Matsuoka, Yasuyuki, Suematsu, Hiroyoshi, Ogawa, Naoki, Miyano, Kenjiro, Kataura, Hiromichi, Maniwa, Yutaka, Suzuki, Shinzo, and Achiba, Yohji

Abstract

We have observed the photoconductive response of film samples of single-walled carbon nanotubes for the first time. Two peaks in the photoconductivity excitation spectra around 0.7 and 1.2 eV are observed at room temperature, which can be interpreted as a photocurrent in semiconducting nanotubes. At a low temperature, we found a marked change in the intensity of the spectrum. In this paper, we discuss this temperature dependence and the mechanism of photoconductivity., identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/4963

Published
2001

13. Gas adsorption in the inside and outside of single-walled carbon nanotubes

Author

Fujiwara, Akihiko, Ishii, Kenji, Suematsu, Hiroyoshi, Kataura, Hiromichi, Maniwa, Yutaka, Suzuki, Shinzou, Achiba, Yohji, Fujiwara, Akihiko, Ishii, Kenji, Suematsu, Hiroyoshi, Kataura, Hiromichi, Maniwa, Yutaka, Suzuki, Shinzou, and Achiba, Yohji

Abstract

Adsorption properties of nitrogen and oxygen gases in single-walled carbon nanotube (SWNT) bundles were investigated by the isotherm and X-ray diffraction (XRD) studies. In the as-grown (AG) nanotubes with close-ended caps, both the gases are adsorbed only in the interstitial channels between triangular packed nanotubes. In the heat-treated (HT) nanotubes with open ends, the gases are adsorbed first in the inside of tubes, and next in the interstitial channels. In each site, gases can be adsorbed with the stoichiometory of C_<20>N_2 or C_<20>O_2 as a monolayer. These results indicate that the inside of nanotube has strong affinity for gas adsorption than the interstitial channels of bundles.

Published
2001

16. Structural basis for the fast phase change of Ge2Sb2Te5: Ring statistics analogy between the crystal and amorphous states

Author

Kohara, Shinji, primary, Kato, Kenichi, additional, Kimura, Shigeru, additional, Tanaka, Hitoshi, additional, Usuki, Takeshi, additional, Suzuya, Kentaro, additional, Tanaka, Hiroshi, additional, Moritomo, Yutaka, additional, Matsunaga, Toshiyuki, additional, Yamada, Noboru, additional, Tanaka, Yoshihito, additional, Suematsu, Hiroyoshi, additional, and Takata, Masaki, additional

Published
2006
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19. C70Molecular Stumbling inside Single-Walled Carbon Nanotubes

Author

Maniwa, Yutaka, primary, Kataura, Hiromichi, additional, Abe, Masatoshi, additional, Fujiwara, Akihiko, additional, Fujiwara, Ryuji, additional, Kira, Hiroshi, additional, Tou, Hideki, additional, Suzuki, Shinzo, additional, Achiba, Yohji, additional, Nishibori, Eiji, additional, Takata, Masaki, additional, Sakata, Makoto, additional, and Suematsu, Hiroyoshi, additional

Published
2003
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26. Photoconductivity of single-walled carbon nanotubes.

Author

Fujiwara, Akihiko, Matsuoka, Yasuyuki, Suematsu, Hiroyoshi, Ogawa, Naoki, Miyano, Kenjiro, Kataura, Hiromichi, Maniwa, Yutaka, Suzuki, Shinzou, and Achiba, Yohji

Subjects
PHOTOCONDUCTIVITY, NANOTUBES, CARBON
Abstract

We have investigated photoconducting properties of mat samples of singlewalled carbon nanotubes (SWNTs) in order to clarify the mechanism of photoconductivity. Two peaks are observed in photoconductivity spectra around 0.7 and 1.2 eV for both samples of SWNTs synthesized by arc discharge and laser ablation methods, which can be interpreted as the photocurrent in the semiconductor phase of nanotubes. No threshold in applied voltage is observed for the occurrence of photoconductivity. Results show that the photoconductivity is an intrinsic feature of SWNTs and that junction areas do not play an important role on photoconductivity. [ABSTRACT FROM AUTHOR]

Published
2001

27. Study on the physical properties of Na[sub 4]C[sub 60].

Author

Takabayashi, Yasuhiro, Kubozono, Yoshihiro, Fujiki, Satoshi, Kashino, Setsuo, Ishii, Kenji, Suematsu, Hiroyoshi, and Ogata, Hironori

Subjects
FULLERENES, EARTH resistance (Geophysics), POLYMERS
Abstract

Temperature dependence of resistivity, ρ, of a two-dimensional polymer phase of Na[sub 4]C[sub 60] has been studied from 190 to 300 K. The ρ was 6.9 x 10³ Ω cm at 300 K, which is higher by six orders than those of metallic fullerides. The temperature dependence of p shows a semiconducting behavior in this temperature region. This result is different from the previous result derived from ESR which suggests a metallic property above 100 K. The gap energy, E[sub g], was estimated to be 0.8 eV. This value is close to those of other A[sub 4]C[sub 60] (A: K, Rb and Cs). [ABSTRACT FROM AUTHOR]

Published
2001

29. Gas Storage in Single-Walled Carbon Nanotubes

Author

Maniwa, Yutaka, primary, Kumazawa, Yoshinori, additional, Saito, Yumi, additional, Tou, Hideki, additional, Kataura, Hiromichi, additional, Ishii, Hiroyoshi, additional, Suzuki, Shinzou, additional, Achiba, Yohji, additional, Fujiwara, Akihiko, additional, and Suematsu, Hiroyoshi, additional

Published
2000
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