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Journal Articles

Quantum paramagnet near spin-state transition

Tomiyasu, Keisuke*; Ito, Naoko*; Okazaki, Ryuji*; Takahashi, Yuki*; Onodera, Mitsugi*; Iwasa, Kazuaki*; Nojima, Tsutomu*; Aoyama, Takuya*; Ogushi, Kenya*; Ishikawa, Yoshihisa*; et al.

Advanced Quantum Technologies (Internet), 1(3), p.1800057_1 - 1800057_7, 2018/12

Spin-state transition, also known as spin crossover, plays a key role in diverse systems. In theory, the boundary range between the low- and high-spin states is expected to enrich the transition and give rise to unusual physical states. However, no compound that realizes a nearly degenerate critical range as the ground state without requiring special external conditions has yet been experimentally identified. This study reports that the Sc substitution in LaCoO3 destabilizes its nonmagnetic low-spin state and generates an anomalous paramagnetic state accompanied by the enhancement of transport gap and magneto-lattice-expansion as well as the contraction of Co-O distance with the increase of electron site transfer. These phenomena are not well described by the mixture of conventional low- and high-spin states, but by their quantum superposition occurring on the verge of a spin-state transition.

Journal Articles

Materials and Life Science Experimental Facility at the Japan Proton Accelerator Research Complex, 3; Neutron devices and computational and sample environments

Sakasai, Kaoru; Sato, Setsuo*; Seya, Tomohiro*; Nakamura, Tatsuya; To, Kentaro; Yamagishi, Hideshi*; Soyama, Kazuhiko; Yamazaki, Dai; Maruyama, Ryuji; Oku, Takayuki; et al.

Quantum Beam Science (Internet), 1(2), p.10_1 - 10_35, 2017/09

Neutron devices such as neutron detectors, optical devices including supermirror devices and $$^{3}$$He neutron spin filters, and choppers are successfully developed and installed at the Materials Life Science Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC), Tokai, Japan. Four software components of MLF computational environment, instrument control, data acquisition, data analysis, and a database, have been developed and equipped at MLF. MLF also provides a wide variety of sample environment options including high and low temperatures, high magnetic fields, and high pressures. This paper describes the current status of neutron devices, computational and sample environments at MLF.

Journal Articles

Weak ferromagnetic ordering disordered by Rh$$^{3+}$$ ions for LaCo$$_{0.8}$$Rh$$_{0.2}$$O$$_{3}$$

Asai, Shinichiro*; Okazaki, Ryuji*; Terasaki, Ichiro*; Yasui, Yukio*; Igawa, Naoki; Kakurai, Kazuhisa

JPS Conference Proceedings (Internet), 3, p.014034_1 - 014034_6, 2014/06

We have carried out the neutron scattering measurements for a single crystal of LaCo$$_{0.8}$$Rh$$_{0.2}$$O$$_{3}$$ in order to investigate the ferromagnetic ordering induced by Rh$$^{3+}$$ substitution for Co$$^{3+}$$ of LaCoO$$_{3}$$. The ordered moment is evaluated to be 0.4$$pm$$0.2$$mu$$$$_{B}$$, which is consistent with the saturation magnetization of LaCo$$_{0.8}$$Rh$$_{0.2}$$O$$_{3}$$. It indicates that the ferromagnetic ordering of LaCo$$_{0.8}$$Rh$$_{0.2}$$O$$_{3}$$ originates from the short-range ferromagnetic ordering disordered by Rh$$^{3+}$$ ions.

Journal Articles

Temperature control system for laser heating; Application for minute asteroidal materials

Osawa, Takahito; Kobayashi, Mikihiko*; Konno, Takeshi*; Egashira, Mitsuru*; Okazaki, Ryuji*; Miura, Yayoi*; Nagao, Keisuke*

Measurement, 50, p.229 - 235, 2014/04

 Times Cited Count:0 Percentile:0.01(Engineering, Multidisciplinary)

A temperature control system for a laser heating has been developed to extract noble gases from minute material samples recovered from the asteroid Itokawa by the Hayabusa spacecraft. An ultra-fine thermocouple was produced from 3% Re-W and 26% Re-W wires 25 $$mu$$m in diameter, and its electromotive force was calibrated. A temperature control program was originally produced using LabVIEW 2011 in which proportional-integral-derivative (PID) control was not adopted as an algorithm of the program. The program controlled the temperature of the tiny samples appropriately. The average temperature during heating was slightly lower than the setting temperature and the standard deviation and the maximum overshoot were lower than 2.5% and 6.0% of the setting temperature, respectively. The performance of the temperature control system is high enough to conduct the stepwise heating experiment for minute extraterrestrial material samples.

Journal Articles

Spin state of Co$$^{3+} $$ in LaCo$$_{1-x}$$ Rh$$_{x}$$O$$_{3}$$ investigated by structural phenomena

Asai, Shinichiro*; Okazaki, Ryuji*; Terasaki, Ichiro*; Yasui, Yukio*; Kobayashi, Wataru*; Nakao, Akiko*; Kobayashi, Kensuke*; Kumai, Reiji*; Nakao, Hironori*; Murakami, Yoichi*; et al.

Journal of the Physical Society of Japan, 82(11), p.114606_1 - 114606_6, 2013/11

 Times Cited Count:6 Percentile:44.56(Physics, Multidisciplinary)

Neutron and synchrotron X-ray diffraction for LaCo$$_{1-x}$$ Rh$$_{x}$$O$$_{3}$$ have been carried out in order to investigate the structural properties related with the spin state of Co$$^{3+}$$ ions. We have found that the values of the Co(Rh)-O bond lengths in the Co(Rh)O$$_{6}$$ octahedron of LaCo$$_{0.8}$$Rh$$_{0.2}$$O$$_{3}$$ are nearly identical at 10 K. The lattice volume for the Rh$$^{3+}$$ substituted samples decreases with the thermal expansion coefficient similar to that of LaCoO$$_{3}$$ from room temperature, and ceases to decrease around 70 K. These experimental results favor a mixed state consisting of the high-spin state and low-spin state Co$$^{3+}$$ ions, and suggest that the high-spin state Co$$^{3+}$$ ions are thermally excited in addition to those pinned by the substituted Rh$$^{3+}$$ ions.

Journal Articles

Construction of a newly designed small-size mass spectrometer for helium isotope analysis; Toward the continuous monitoring of $$^{3}$$He/$$^{4}$$He ratios in natural fluids

Bajo, Kenichi*; Sumino, Hirochika*; Toyoda, Michisato*; Okazaki, Ryuji*; Osawa, Takahito; Ishihara, Morio*; Katakuse, Itsuo*; Notsu, Kenji*; Igarashi, Joji*; Nagao, Keisuke*

Mass Spectrometry (Internet), 1(2), p.A0009_1 - A0009_10, 2012/11

The construction of a small-size, magnetic sector, single focusing mass spectrometer (He-MS) for the continuous, on-site monitoring of the He isotope ratio ($$^{3}$$He/$$^{4}$$He) is described. The instrument is capable of measuring $$^{4}$$He/$$^{20}$$Ne ratios dissolved in several different types of natural fluids of geochemical interest, such as groundwater and gas from hot springs, volcanoes and gas well fields. Ion optics of the He-MS was designed by using the ion trajectory simulation program TRIO so as to measure $$^{3}$$He and $$^{4}$$He simultaneously with a double collector system under mass resolution power of $$>$$ 500. Presently attained specifications of the He-MS are; (1) mass resolving power of ca. 490, enough to separate $$^{3}$$He$$^{+}$$ from interfering ions, HD$$^{+}$$ and H$$_{3}$$$$^{+}$$, (2) ultra-high vacuum condition, and (3) high sensitivity enough to detect $$^{3}$$He amount 3000000 atoms).

Journal Articles

Irradiation history of Itokawa regolith material deduced from noble gases in the Hayabusa samples

Nagao, Keisuke*; Okazaki, Ryuji*; Nakamura, Tomoki*; Miura, Yayoi*; Osawa, Takahito; Bajo, Kenichi*; Matsuda, Shintaro*; Ebihara, Mitsuru*; Ireland, T.*; Kitajima, Fumio*; et al.

Science, 333(6046), p.1128 - 1131, 2011/08

 Times Cited Count:125 Percentile:95.52(Multidisciplinary Sciences)

A steroid surface materials record regolith processes and a history of cosmic-ray irradiation. Noble gas isotopes in three rocky grains from Itokawa have been determined. High concentrations of solar He, Ne, and Ar, as high as those in lunar soils, are released at variable temperatures from each sample. The isotopic compositions are essentially identical to those of solar wind but distinguishable in He relative abundance. These noble gas characteristics can be explained by repeated implantation and preferential loss of solar He by removal of weathered He-rich rim on the grain surface through friction among regolith grains on Itokawa. Residence time of regolith materials on Itokawa is alculated to be shorter than 10 Myr, suggesting that regolith materials of small asteroids would escape easily to space.

Journal Articles

Anomalous low-field diamagnetic response in ultraclean URu$$_2$$Si$$_2$$ superconductor

Okazaki, Ryuji*; Shimozawa, Masaaki*; Shishido, Hiroaki*; Konczykowski, M.*; Haga, Yoshinori; Matsuda, Tatsuma; Yamamoto, Etsuji; Onuki, Yoshichika; Yanase, Yoichi*; Shibauchi, Takasada*; et al.

Journal of Physics; Conference Series, 273, p.012081_1 - 012081_4, 2011/02

 Times Cited Count:3 Percentile:64

Journal Articles

Rotational symmetry breaking in the hidden-order phase of URu$$_2$$Si$$_2$$

Okazaki, Ryuji*; Shibauchi, Takasada*; Shi, H. J.*; Haga, Yoshinori; Matsuda, Tatsuma; Yamamoto, Etsuji; Onuki, Yoshichika; Ikeda, Hiroaki*; Matsuda, Yuji*

Science, 331(6016), p.439 - 442, 2011/01

 Times Cited Count:206 Percentile:98.06(Multidisciplinary Sciences)

Journal Articles

Lower critical fields and the anisotropy in PrFeAsO$$_{1-y}$$ single crystals

Okazaki, Ryuji*; Konczykowski, M.*; Van der Beek, C. J.*; Kato, Tomonari*; Hashimoto, Kenichiro*; Shimozawa, Masaaki*; Shishido, Hiroaki*; Yamashita, Minoru*; Ishikado, Motoyuki; Kito, Hijiri*; et al.

Physica C, 470(Suppl.1), p.S485 - S486, 2010/12

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

We report the lower critical fields $$H_{c1}$$ measurements on Fe-based oxipnictide PrFeAsO$$_{1-y}$$ single crystals for $$H$$ $$parallel$$ $$c$$ and $$H$$ $$parallel$$ $$ab$$-planes. To avoid the difficulty of $$H_{c1}$$ determinations due to the flux pinning, we developed a novel method using a miniature hall-sensor array which can evaluate the local magnetic induction ai each sensor position. The hall sensor which is placed on the edge of the crystal clearly resolves the first flux penetration from the Meissner state. The temperature dependence of $$H_{c1}$$ for $$H$$ $$parallel$$ $$c$$ is well scaled by the in-plane penetration depth and is consistent with a full-gap superconducting state. The anistropy of $$H_{c1}$$ at low temperatures is estimated to be $$sim$$ 3, which is much smaller than of $$H_{c2}$$. This indicates the multiband superconductivity, in which the active bands for superconductivity are more two-dimensional.

Journal Articles

Disorder and flux pinning in superconducting pnictide single crystals

Van der Beek, C. J.*; Rizza, G.*; Konczykowski, M.*; Fertey, P.*; Monnet, I.*; Okazaki, Ryuji*; Kato, Tomonari*; Hashimoto, Kenichiro*; Shimozawa, Masaaki*; Shishido, Hiroaki*; et al.

Physica C, 470(Suppl.1), p.S385 - S386, 2010/12

 Times Cited Count:1 Percentile:6.71(Physics, Applied)

Crystalline disorder in the pnictide superconductor PrFeAsO$$_{1-x}$$ is studied using magneto-optical visualisation of flux penetration, transmission electron microscopy, and X-ray diffraction using synchrotron radiation. Critical-state like flux distributions and the magnitude and temperature dependence of the critical current demonstrate bulk vortex pinning by oxygen vacancies at all temperatures.

Journal Articles

Exotic superconducting state embedded in the hidden order state of URu$$_2$$Si$$_2$$

Matsuda, Yuji*; Okazaki, Ryuji*; Kasahara, Yuichi*; Shishido, Hiroaki*; Shibauchi, Takasada*; Haga, Yoshinori; Matsuda, Tatsuma; Onuki, Yoshichika

Physica C, 470(20), p.1013 - 1017, 2010/11

 Times Cited Count:1 Percentile:6.71(Physics, Applied)

Journal Articles

Anomalous temperature dependence of lower critical field in ultraclean URu$$_2$$Si$$_2$$

Okazaki, Ryuji*; Shimozawa, Masaaki*; Shishido, Hiroaki*; Konczykowski, M.*; Haga, Yoshinori; Matsuda, Tatsuma; Yamamoto, Etsuji; Onuki, Yoshichika; Yanase, Yoichi*; Shibauchi, Takasada*; et al.

Journal of the Physical Society of Japan, 79(8), p.084705_1 - 084705_7, 2010/08

 Times Cited Count:15 Percentile:65.57(Physics, Multidisciplinary)

Journal Articles

Flux pinning in PrFeAsO$$_{0.9}$$ and NdFeAsO$$_{0.9}$$F$$_{0.1}$$ superconducting crystals

Van der Beek, C. J.*; Rizza, G.*; Konczykowski, M.*; Fertey, P.*; Monnet, I.*; Klein, T.*; Okazaki, Ryuji*; Ishikado, Motoyuki; Kito, Hijiri*; Iyo, Akira*; et al.

Physical Review B, 81(17), p.174517_1 - 174517_11, 2010/05

 Times Cited Count:95 Percentile:93.76(Materials Science, Multidisciplinary)

Local magnetic measurements are used to quantitatively characterize heterogeneity and flux line pinning in PrFeAsO$$_{1-y}$$ and NdFeAs(O,F)superconducting single crystals. In spite of spatial fluctuations of the critical current density on the macroscopic scale, it is shown that the major contribution comes from collective pinning of vortex lines by microscopic defects by the mean-free path fluctuation mechanism. The defect density extracted from experiment corresponds to the dopant atom density, which means that dopant atoms play an important role both in vortex pinning and in quasi-particle scattering.

Journal Articles

Lower critical fields of superconducting PrFeAsO$$_{1-y}$$ single crystals

Okazaki, Ryuji*; Konczykowski, M.*; Van der Beek, C. J.*; Kato, Tomonari*; Hashimoto, Kenichiro*; Shimozawa, Motoyuki*; Shishido, Hiroaki*; Yamashita, Minoru*; Ishikado, Motoyuki; Kito, Hijiri*; et al.

Physical Review B, 79(6), p.064520_1 - 064520_6, 2009/02

 Times Cited Count:57 Percentile:87.43(Materials Science, Multidisciplinary)

We have studied the lower critical fields H$$_{c1}$$ of superconducting iron oxipnictide PrFeAsO$$_{1-y}$$ single crystals for H parallel and perpendicular to the ab-planes.

Journal Articles

Flux line lattice melting and the formation of a coherent quasiparticle bloch state in the ultraclean URu$$_2$$Si$$_2$$ superconductor

Okazaki, Ryuji*; Kasahara, Yuichi*; Shishido, Hiroaki*; Konczykowski, M.*; Behnia, K.*; Haga, Yoshinori; Matsuda, Tatsuma; Onuki, Yoshichika; Shibauchi, Takasada*; Matsuda, Yuji*

Physical Review Letters, 100(3), p.037004_1 - 037004_4, 2008/01

 Times Cited Count:27 Percentile:76.24(Physics, Multidisciplinary)

Oral presentation

The Development of the magnetic order in multiferroic material NdCrTiO$$_{5}$$ revealed by the neutron diffraction study

Kori, Shunsuke*; Igarashi, Taichi*; Okazaki, Ryuji*; Taniguchi, Hiroki*; Tanisaki, Ichiro*; Yasui, Yukio*; Igawa, Naoki; Hoshikawa, Akinori*; Ishigaki, Toru*

no journal, , 

The neutron powder diffraction for the multiferroic material, NdCrTiO$$_{5}$$ has been carried out to investigate the development of the magnetic order in the material. We found the intensities of magnetic peaks increased with decreasing temperature below the transition temperature T$$_{N}$$. We discuss temperate dependence of magnetic moments and the development of magnetic order.

Oral presentation

Muonic X-ray analysis for Ryugu samples

Osawa, Takahito; Ninomiya, Kazuhiko*; Nakamura, Tomoki*; Takahashi, Tadayuki*; Terada, Kentaro*; Yurimoto, Hisayoshi*; Noguchi, Takaaki*; Okazaki, Ryuji*; Yabuta, Hikaru*; Naraoka, Hiroshi*; et al.

no journal, , 

I report on the muonic X-ray analysis experiment conducted at J-PARC from 2020 to 2021, in which the analytical method was significantly developed through four preliminary experiments and successfully analyzed samples from the asteroid Ryugyu in July 2021. The experimental process is described from a radiochemical point of view.

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