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Journal Articles

Intrinsic 2D ferromagnetism in V$$_{5}$$Se$$_{8}$$ epitaxial thin films

Nakano, Masaki*; Wang, Y.*; Yoshida, Satoshi*; Matsuoka, Hideki*; Majima, Yuki*; Ikeda, Keisuke*; Hirata, Yasuyuki*; Takeda, Yukiharu; Wadachi, Hiroki*; Kohama, Yoshimitsu*; et al.

Nano Letters, 19(12), p.8806 - 8810, 2019/12

 Times Cited Count:22 Percentile:91.07(Chemistry, Multidisciplinary)

Journal Articles

Electronic structure of the high-$$T_{rm C}$$ ferromagnetic semiconductor (Ga,Fe)Sb; X-ray magnetic circular dichroism and resonance photoemission spectroscopy studies

Sakamoto, Shoya*; Tu, N. T.*; Takeda, Yukiharu; Fujimori, Shinichi; Hai, P. N.*; Anh, L. D.*; Wakabayashi, Yuki K.*; Shibata, Goro*; Horio, Masafumi*; Ikeda, Keisuke*; et al.

Physical Review B, 100(3), p.035204_1 - 035204_8, 2019/07

Journal Articles

Electronic structure of the high-$$T_{rm C}$$ ferromagnetic semiconductor (Ga,Fe)Sb; X-ray magnetic circular dichroism and resonance photoemission spectroscopy studies

Sakamoto, Shoya*; Tu, N. T.*; Takeda, Yukiharu; Fujimori, Shinichi; Hai, P. N.*; Anh, L. D.*; Wakabayashi, Yuki*; Shibata, Goro*; Horio, Masafumi*; Ikeda, Keisuke*; et al.

Physical Review B, 100(3), p.035204_1 - 035204_8, 2019/07

 Times Cited Count:8 Percentile:67.98(Materials Science, Multidisciplinary)

Journal Articles

Local magnetic states of the weakly ferromagnetic iron-based superconductor Sr$$_{2}$$VFeAsO$$_{3-delta}$$ studied by X-ray magnetic circular dichroism

Horio, Masafumi*; Takeda, Yukiharu; Namiki, Hiromasa*; Katagiri, Takao*; Wakabayashi, Yuki*; Sakamoto, Shoya*; Nonaka, Yosuke*; Shibata, Goro*; Ikeda, Keisuke*; Saito, Yuji; et al.

Journal of the Physical Society of Japan, 87(10), p.105001_1 - 105001_2, 2018/10

 Times Cited Count:1 Percentile:16.87(Physics, Multidisciplinary)

Journal Articles

Cation distribution and magnetic properties in ultrathin (Ni$$_{1-x}$$Co$$_{x}$$)Fe$$_{2}$$O$$_{4}$$ (x=0-1) layers on Si(111) studied by soft X-ray magnetic circular dichroism

Wakabayashi, Yuki*; Nonaka, Yosuke*; Takeda, Yukiharu; Sakamoto, Shoya*; Ikeda, Keisuke*; Chi, Z.*; Shibata, Goro*; Tanaka, Arata*; Saito, Yuji; Yamagami, Hiroshi; et al.

Physical Review Materials (Internet), 2(10), p.104416_1 - 104416_12, 2018/10

 Times Cited Count:6 Percentile:37.83(Materials Science, Multidisciplinary)

Journal Articles

Observation of all-in type tetrahedral displacements in nonmagnetic pyrochlore niobates

Torigoe, Shuhei*; Ishimoto, Yutaro*; Aoishi, Yuhei*; Murakawa, Hiroshi*; Matsumura, Daiju; Yoshii, Kenji; Yoneda, Yasuhiro; Nishihata, Yasuo; Kodama, Katsuaki; Tomiyasu, Keisuke*; et al.

Physical Review B, 93(8), p.085109_1 - 085109_5, 2016/02

 Times Cited Count:4 Percentile:26.78(Materials Science, Multidisciplinary)

Journal Articles

Magnetic properties of single crystalline YbFe$$_{2}$$O$$_{4}$$

Yoshii, Kenji; Mizumaki, Masaichiro*; Matsumoto, Keisuke*; Mori, Shigeo*; Endo, Naruki; Saito, Hiroyuki; Matsumura, Daiju; Kambe, Takashi*; Ikeda, Naoshi*

Journal of Physics; Conference Series, 428, p.012032_1 - 012032_5, 2013/04

 Times Cited Count:13 Percentile:97.61

We have investigated a single crystal of multiferroic YbFe$$_{2}$$O$$_{4}$$. Its magnetic transition temperature was 250 K. The magnetization along the c-axis was much larger than that within the ab plane, indicating the Ising character of this system. The field-cooled magnetization became negative below 10 K. This was explained in terms of an antiparallel coupling between Yb and Fe moments. Magnetocaloric effects were also observed. The change of entropy was found to show a broad peak with a width of 100 K, which is favorable to application.

Journal Articles

Role of residual transition-metal atoms in oxygen reduction reaction in cobalt phthalocyanine-based carbon cathode catalysts for polymer electrolyte fuel cell

Kobayashi, Masaki*; Niwa, Hideharu*; Harada, Yoshihisa*; Horiba, Koji*; Oshima, Masaharu*; Ofuchi, Hironori*; Terakura, Kiyoyuki*; Ikeda, Takashi; Koshigoe, Yuka*; Ozaki, Junichi*; et al.

Journal of Power Sources, 196(20), p.8346 - 8351, 2011/10

 Times Cited Count:32 Percentile:70.76(Chemistry, Physical)

The electronic structure of Co atoms in CoPc-based carbon catalysts, which were prepared by pyrolyzing a mixture of CoPc and phenol resin polymer up to 1000$$^circ$$C, has been investigated using XAFS analysis and HXPES. The Co K XAFS spectra show that most of the Co atoms are in the metallic state and small quantities of oxidized Co components are present in the samples even after acid washing to remove Co atoms. Based on the difference in probing depth between XAFS and HXPES, it was found that after acid washing, the surface region with the aggregated Co clusters is primarily composed of metallic Co. Since the electrochemical properties remain almost unchanged even after the acid washing process, the residual metallic and oxidized Co atoms themselves will hardly contribute to the ORR activity of the CoPc-based carbon cathode catalysts, implying that the active sites of the CoPc-based catalysts primarily consist of light elements such as C and N.

Journal Articles

Doping effect on charge ordered structure in Mn-doped YbFe$$_{2}$$O$$_{4}$$

Matsumoto, Keisuke*; Koyama, Tsukasa*; Mori, Shigeo*; Yoshii, Kenji; Kambe, Takashi*; Ikeda, Naoshi*

IOP Conference Series; Materials Science and Engineering, 18(9), p.092047_1 - 092047_4, 2011/09

 Times Cited Count:0 Percentile:0.09

Changes of charge ordered (CO) structure by partial substitution of Mn for Fe in YbFe$$_{2}$$O$$_{4}$$ were investigated by a transmission electron microscope (TEM), incombination with conventional dielectric measurement. It is revealed that partial substitution of Mn$$^{2+}$$ for Fe$$^{2+}$$ in YbFe$$_{2}$$O$$_{4}$$ destroyed drastically the CO structure with the wave vector of q=$$<$$1/3 1/3 1/2$$>$$. Consequently polar clustering structure giving rise to honeycomb-shaped diffuse streaks was found in YbFeMnO$$_{4}$$. The random distribution of polar clustering structure gives rise to characteristic broad dielectric dispersion.

Journal Articles

Collapsing processes of charge ordered structure in charge- and spin- frustrated ferrite YbFe$$_{2}$$O$$_{4}$$

Matsumoto, Keisuke*; Koyama, Tsukasa*; Mori, Shigeo*; Yoshii, Kenji; Ikeda, Naoshi*

Journal of Physics; Conference Series, 320, p.012085_1 - 012085_5, 2011/09

 Times Cited Count:0 Percentile:0.03

In order to clarify the stability of charge ordered structure (CO) in charge- and spinfrustrated ferrite YbFe$$_{2}$$O$$_{4}$$, we have investigated changes of the CO structure by partial substitution of Mn$$^{2+}$$ for Fe$$^{2+}$$ in YbFe$$_{2}$$O$$_{4}$$ by a transmission electron microscope (TEM), incombination with conventional dielectric measurement. It is revealed that subtle substitution of Mn$$^{2+}$$ for Fe$$^{2+}$$ in YbFe$$_{2}$$O$$_{4}$$ destroyed drastically the CO structure with the wave vector of q=$$<$$1/3 1/3 1/2$$>$$ and, instead, induced polar clustering structure characterized by honeycomb shaped diffuse scatterings in the reciprocal space. The formation of polar clustering structure should be responsible for the characteristic dielectric dispersion.

Journal Articles

X-ray photoemission spectroscopy analysis of N-containing carbon-based cathode catalysts for polymer electrolyte fuel cells

Niwa, Hideharu*; Kobayashi, Masaki*; Horiba, Koji*; Harada, Yoshihisa*; Oshima, Masaharu*; Terakura, Kiyoyuki*; Ikeda, Takashi; Koshigoe, Yuka*; Ozaki, Junichi*; Miyata, Seizo*; et al.

Journal of Power Sources, 196(3), p.1006 - 1011, 2011/02

 Times Cited Count:80 Percentile:92(Chemistry, Physical)

We report on the electronic structure of three different types of N-containing carbon-based cathode catalysts for polymer electrolyte fuel cells observed by hard X-ray photoemission spectroscopy. C 1s spectra show the importance of $$sp^{2}$$ carbon network formation for the oxygen reduction reaction (ORR) activity. Samples having high oxygen reduction reaction activity in terms of oxygen reduction potential contain high concentration of graphite-like nitrogen. Based on a quantitative analysis of our results, the oxygen reduction reaction activity of the carbon-based cathode catalysts will be improved by increasing concentration of graphite-like nitrogen in a developed $$sp^{2}$$ carbon network.

Journal Articles

Band structure and fermi surface of uranium compounds; Soft X-ray angle-resolved photoemission study

Fujimori, Shinichi; Terai, Kota; Takeda, Yukiharu; Okane, Tetsuo; Saito, Yuji; Kobayashi, Keisuke; Fujimori, Atsushi; Yamagami, Hiroshi*; Ikeda, Shugo; Matsuda, Tatsuma; et al.

Journal of the Physical Society of Japan, 75(Suppl.), p.99 - 101, 2006/08

 Times Cited Count:0 Percentile:0(Physics, Multidisciplinary)

In the present study, we have performed SX-ARPES experiments on some heavy Fermion (HF) uranium compounds such as UPd$$_2$$Al$$_3$$ using soft X-ray synchrotron radiation from BL23SU of SPring-8. UPd$$_2$$Al$$_3$$ is an HF uranium compound which has transitions into an antiferromagnetic phase at $$T_{rm N} =14$$ K and into a superconducting phase at $$T_{rm C}$$=2 K. To describe the various properties of this compound, the dual model for U 5$$f$$ states is proposed. In this model, two of the three U 5f states are in a localized state while the third electron has delocalized character. We have obtained U 5f sensitive band structure of UPd$$_2$$Al$$_3$$ by SX-ARPES, and the results are compared with this scenario. Temperature dependence of the U 5$$f$$ electronic structure in this compound is also discussed.

Journal Articles

Magnetic structure of CoO studied by neutron and synchrotron X-ray diffraction

Tomiyasu, Keisuke*; Inami, Toshiya; Ikeda, Naoshi*

Physical Review B, 70(11), p.184411_1 - 184411_6, 2004/11

 Times Cited Count:40 Percentile:83.1(Materials Science, Multidisciplinary)

Below $$T$$$$_{N}$$ = 289 K, the antiferromagnet CoO exhibits magnetic long-range order described by a propagation vector along the trigonal axis, whereas the lattice is distorted monoclinicly along both the tetragonal and the trigonal axes. In order to elucidate this inconsistency, we performed neutron and synchrotron X-ray diffraction experiments on single crystals of CoO, and found a new series of magnetic reflections represented by a propagation vector along the tetragonal axis below $$T$$$$_{N}$$N. These results suggest an altered magnetic structure of CoO, which includes both the trigonal and the tetragonal propagation vectors, has a monoclinic symmetry and which is in accordance with the distorted lattice symmetry.

Journal Articles

A Natural attenuation of arsenic in drainage from an abandoned arsenic mine dump

Fukushi, Keisuke*; Sasaki, Miwa*; Sato, Tsutomu*; Yanase, Nobuyuki; Amano, Hikaru; Ikeda, Hodaka*

Applied Geochemistry, 18(8), p.1267 - 1278, 2003/08

 Times Cited Count:197 Percentile:96.12(Geochemistry & Geophysics)

At Nishinomaki abandoned mine district, the water is acidic and contains much amounts of arsenic. However, arsenic concentration decreases downward without any artificial treatment. To understand the mechanism of the natural attenuation, the acid mine drainage and the ochreous precipitates were collected. The samples were analyzed by XRD, IR, ICP-MS and ion-chromatograph. The precipitates were investigated by selective extraction procedure. These results were interpreted with those calculated by the geochemical code. The contamination of water has been result from oxidation of pyrite and realgar and subsequent release of iron. The released ferrous iron transforms to ferric form by bacterial oxidation and then schwertmannite forms immediately. While the arsenic concentrations in the stream are lowered to background level at downstream, these in the ochreous precipitates are up to 60 mg/g. The iron hydroxide has been known to exhibit the high sorption affinity to arsenate. Hence, arsenic is effectively removed by the schwertmannite from the contaminated water and attenuated naturally.

Journal Articles

Wave accessibility effects on lower hybrid current drive in JT-60U

Ikeda, Yoshitaka; Naito, Osamu; Ushigusa, Kenkichi; Sato, Masayasu; Kondoh, Takashi; Ide, Shunsuke; Seki, Masami; Nagashima, Keisuke; S.W.Wolfe*; Asakura, Nobuyuki; et al.

Nuclear Fusion, 34(6), p.871 - 880, 1994/00

 Times Cited Count:11 Percentile:40.51(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

LHRF current drive experiments on JT-60

Imai, Tsuyoshi; Ushigusa, Kenkichi; Ikeda, Yoshitaka; Naito, Osamu; Yoshida, Hidetoshi; Seki, Masami; Itami, Kiyoshi; Nagashima, Keisuke; Uehara, Kazuya; Nagashima, Takashi

Kaku Yugo Kenkyu, 65(SPECIAL ISSUE), p.99 - 118, 1991/03

no abstracts in English

Journal Articles

Observation of limiter H mode in the JT-60 tokamak with lower hybrid current drive

Tsuji, Shunji; Ushigusa, Kenkichi; Ikeda, Yoshitaka; Imai, Tsuyoshi; Itami, Kiyoshi; Nemoto, Masahiro; Nagashima, Keisuke; Koide, Yoshihiko; Kawano, Yasunori; Fukuda, Takeshi; et al.

Physical Review Letters, 64(9), p.1023 - 1026, 1990/02

 Times Cited Count:54 Percentile:88.46(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

Simultaneous heating by high power lower hybrid waves and neutral beams in the JT-60 tokamak

Ushigusa, Kenkichi; Imai, Tsuyoshi; Ikeda, Yoshitaka; Sakamoto, Keishi; F.X.Soeldner*; *; Tsuji, Shunji; Shimizu, Katsuhiro; Naito, Osamu; Uehara, Kazuya; et al.

Nuclear Fusion, 29(2), p.265 - 276, 1989/02

 Times Cited Count:16 Percentile:58.11(Physics, Fluids & Plasmas)

no abstracts in English

JAEA Reports

Lower hybrid wave heating into neutral beam heated plasma in the JT-60 tokamak

Ushigusa, Kenkichi; Imai, Tsuyoshi; Ikeda, Yoshitaka; Sakamoto, Keishi; F.X.Soldner*; *; Tsuji, Shunji; Shimizu, Katsuhiro; Naito, Osamu; Uehara, Kazuya; et al.

JAERI-M 88-115, 28 Pages, 1988/06

JAERI-M-88-115.pdf:0.87MB

no abstracts in English

Oral presentation

Soft X-ray angle resolved photoemission study of UPd$$_2$$Al$$_3$$

Fujimori, Shinichi; Okane, Tetsuo; Saito, Yuji; Kobayashi, Keisuke; Fujimori, Atsushi; Yamagami, Hiroshi; Ikeda, Shugo; Matsuda, Tatsuma; Haga, Yoshinori; Yamamoto, Etsuji; et al.

no journal, , 

no abstracts in English

25 (Records 1-20 displayed on this page)