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Tomiyasu K.,Tohoku University | Kamazawa K.,Research Center for Neutron Science and Technology | Kamazawa K.,Japan Atomic Energy Agency
Journal of the Physical Society of Japan | Year: 2011

We analyzed the single-crystal neutron scattering data on a frustrated spinel ZnFe 2O 4, which is governed by dominant antiferromagnetic third-neighbor exchange interactions J 3 and additional ferromagnetic J 1 [K. Kamazawa et al.: Phys. Rev. B 68 (2003) 024412]. A spin dodecamer model that is formed on the kagome plane is proposed. It is notable that, although J 3 bonds consist of two types of exchange paths Fe-O-Fe-O-Fe and Fe-O-Zn-O-Fe, only the spatial spin correlations corresponding to the former paths are antiferromagnetic while those of all the latter paths are ferromagnetic in the dodecamer. This fact suggests that the frustration is relieved by utilizing the difference of exchange paths even in the same-distant interactions, that is to say, that only specific orbital mixing is selectively enhanced as an origin of the spin molecule. © 2011 The Physical Society of Japan.

Abe H.,Japan National Defense Academy | Takekiyo T.,Japan National Defense Academy | Shigemi M.,Japan National Defense Academy | Yoshimura Y.,Japan National Defense Academy | And 5 more authors.
Journal of Physical Chemistry Letters | Year: 2014

The direct evidence of confined water ("water pocket") inside hydrophilic room-temperature ionic liquids (RTILs) was obtained by complementary use of small-angle X-ray scattering and small-angle neutron scattering (SAXS and SANS). A large contrast in X-ray and neutron scattering cross-section of deuterons was used to distinguish the water pocket from the RTIL. In addition to nanoheterogeneity of pure RTILs, the water pocket formed in the water-rich region. Both water concentration and temperature dependence of the peaks in SANS profiles confirmed the existence of the hidden water pocket. The size of the water pocket was estimated to be ∼3 nm, and D2O aggregations were well-simulated on the basis of the observed SANS data. © 2014 American Chemical Society.

Okuda T.,Kagoshima University | Kajimoto R.,Research Center for Neutron Science and Technology | Okawa M.,Tokyo University of Science | Saitoh T.,Tokyo University of Science
International Journal of Modern Physics B | Year: 2013

In this review, we will discuss the effects of itinerant hole and disorder produced by substitutions on the magnetic states of polycrystalline delafossite oxide CuCrO2 having a spin-3/2 antiferromagnetic triangular sublattice. First, we will show the effects of hole-doping by the substitution of nonmagnetic Mg2+ for magnetic Cr3+ on the physical properties of CuCrO2, and will discuss the origin of nontrivial promotion of the 120° Néel state due to the coupling between the itinerant hole and localized spin. Next, we will show the effects of disorder introduced by the isovalent substitutions such as the nonmagnetic Ag+ substitution for nonmagnetic Cu+ and the nonmagnetic Al3+ one for magnetic Cr3+, and will discuss the possibility of appearance of unusual magnetic states such as spin liquid or spin nematic states. © 2013 World Scientific Publishing Company.

Purevjav N.,Okayama University | Okuchi T.,Okayama University | Tomioka N.,Okayama University | Tomioka N.,Japan Agency for Marine - Earth Science and Technology | And 3 more authors.
Geophysical Research Letters | Year: 2014

Hydrogen site positions and occupancies in the crystal structure of synthetic hydrous ringwoodite have been determined for the first time by high-resolution neutron powder diffraction conducted at the pulsed neutron source at Japan Proton Accelerator Research Complex (J-PARC). It is demonstrated that hydrogen exchanges not only with Mg or Fe but also with Si cations to form hydroxyl and hydrogen bonding, both within the relevant octahedra or tetrahedra created by their surrounding oxygen anions. The hydrated octahedra shrink, whereas the hydrated tetrahedra expand. The occurrence of simultaneous hydration of octahedra and tetraheda is thus unambiguously confirmed, whereby the latter plays an especially unique role in reducing seismic velocity and for enhancing the electrical conductivity of ringwoodite at high pressures and temperatures. These results provide distinctive implications for discussing the physical properties of hydrous ringwoodite occurring in the mantle transition zone and evaluating the actual water content in the zone. Key Points Hydrogen site positions in ringwoodite crystal structure are first determinedHydrogen exchanges not only with Mg or Fe but also with Si in the structureThe nature of deep mantle water stored in the transition zone is revealed ©2014. American Geophysical Union. All Rights Reserved.

Lee S.C.,University of Tokyo | Ueda A.,University of Tokyo | Kamo H.,University of Tokyo | Takahashi K.,Kobe University | And 9 more authors.
Chemical Communications | Year: 2012

A unique N+-H⋯N hydrogen-bonded (H-bonded) dimer motif based on partially oxidized pyridyl-substituted TTF was constructed in the charge-transfer complex. The charge ordering in the TTF column by the charge disproportionation in the dimer regulates the arrangement of the H-bonded proton, evidencing the proton-electron coupled state. © 2012 The Royal Society of Chemistry.

Motoya K.,Tokyo University of Science | Moyoshi T.,Tokyo University of Science | Moyoshi T.,Research Center for Neutron Science and Technology | Matsuda M.,Oak Ridge National Laboratory
Journal of the Physical Society of Japan | Year: 2014

A long-time variation in the magnetic structure of Ce0.98La 0.02Ir3Si2 has been studied by magnetization and timeresolved neutron scattering measurements. CeIr3Si2 is the first material in which the long-time variation in magnetic structure was observed in three-dimensional uniform magnets. Similar long-time variations in magnetic structure have been observed in several uniform materials. In order to clarify whether the long-time variations in the magnetic structure of these materials do not originate from randomness due to unexpected impurities or imperfections, the time variation behavior in a material with embedded randomness has been examined. The time variations observed in the magnetization and neutron scattering measurements of Ce0.98La0.02Ir 3Si2 are basically the same as those observed in CeIr 3Si2. Present results have shown that a peculiar long-time variation in the magnetic structure of CeIr3Si2 is not caused by inevitable randomness in a sample but is its intrinsic property. © 2014 The Physical Society of Japan.

Lee S.C.,University of Tokyo | Ueda A.,University of Tokyo | Nakao A.,Research Center for Neutron Science and Technology | Kumai R.,High Energy Accelerator Research Organization | And 3 more authors.
Chemistry - A European Journal | Year: 2014

Protonated pyridyl-substituted tetrathiafulvalene electron-donor molecules (PyH+-TTF) showed significant changes in the electron-donating ability and HOMO-LUMO energy gap compared to the neutral analogues and gave a unique N+-H...N hydrogen-bonded (H-bonded) dimer unit in the proton-electron correlated charge-transfer (CT) complex crystals. We have evaluated these features from the viewpoint of the molecular structure of the PyH+-TTF derivatives, that is, the substitution position of the Py group and/or the presence or absence of the ethylenedithio (EDT) group. Among 2-PyH+-TTF (1 oH+), 3-PyH+-TTF (1 mH +), 4-PyH+-TTF (1 pH+), and 4-PyH +-EDT-TTF (2 pH+) systems, the para-pyridyl-substituted donors 1 pH+ and 2 pH+ exhibit more marked changes upon protonation in solution; a larger redshift in the intramolecular CT absorption band and a larger decrease in the electron-donating ability. Furthermore, the EDT system 2 pH+ has the smallest intramolecular Coulombic repulsion energy. These differences are reasonably interpreted by considering the energy levels and distributions of the HOMO and LUMO obtained by quantum chemical calculations. Such substituent effects related to protonation were also examined by comparing the structure and properties of a new H-bonded CT complex crystal based on 2 pH+ with those of its 1 pH+ analogue recently prepared by us: Both of them form a similar type of H-bonded dimer unit, however, its charge distribution as well as the overall molecular arrangement, electronic structure, and conductivity were significantly modulated by the introduction of the EDT group. These results provide a new insight into the structural and electronic features of the PyH+-TTF-based proton-electron correlated molecular conductors. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Su Y.,Ibaraki University | Tomota Y.,Ibaraki University | Suzuki J.,Research Center for Neutron Science and Technology | Ohnuma M.,Japan National Institute of Materials Science
ISIJ International | Year: 2011

The behavior of hydrogen in an ultrafine-grained electrodeposited pure iron with Lankford (r) value larger than 7.0 was studied by small angle neutron scattering (SANS) and thermal desorption spectroscopy (TDS). Nano-sized inhomogeneity consisting of hydrogen bubble exists in the deposited specimen. The bubble size increases a little by 673 K annealing and then all the bubbles disappear after 973 K annealing. With rolling at room temperature (RT), the bubble size and number density are found to decrease, which must be caused by the change in the status of hydrogen location during plastic deformation. Crystal rotation and grain coalescence are revealed to occur after rolling deformation from electron backscattered diffraction (EBSD) results. © 2011 ISIJ.

Kobayashi Y.,Nagoya University | Kototani S.,Nagoya University | Ohishi K.,Research Center for Neutron Science and Technology | Itoh M.,Nagoya University | And 3 more authors.
Journal of the Physical Society of Japan | Year: 2015

87Rb NMR, muon spin relaxation (μSR), and neutron diffraction studies have been carried out to investigate how the superconducting (SC) fraction is determined in RbxFe2-ySe2 samples. We observe several phases with different compositions, crystal structures, and magnetic properties of each sample. Samples containing a phase with superconductivity (SC phase) are separated into two phases, an antiferromagnetic (AFM) phase with the block-type antiferromagnetism (AFM1 phase; space group I4=m, Néel temperature TN1 ∼ 550 K) and the SC phase (I4=mmm, SC transition temperature Tc ∼ 30 K). This SC phase has a very small amount of Fe vacancies, if any. In samples having no SC phase, besides the AFM1 phase, there are two other phases, an AFM phase (AFM2 phase; Pmna, TN2 ∼ 150 K) and a phase with an appreciable amount of Fe vacancy (I4=mmm; non-SC phase). Thus, the presence of the coexisting phases is an origin of the complicated physical behavior dependent on the (x; y) values observed in the RbxFe2-ySe2 samples. ©2015 The Physical Society of Japan

Kobayashi Y.,Nagoya University | Kototani S.,Nagoya University | Itoh M.,Nagoya University | Sato M.,Research Center for Neutron Science and Technology
Journal of Physics: Conference Series | Year: 2014

Samples of RbxFe2-ySe2 exhibiting superconductivity [superconducting (SC) samples] undergo a phase-separation into two phases, a Fe-vacancy ordered phase with antiferromagnetic (AFM) transition at TN1∼500 K (AFM1 phase) and a phase with little Fe- vacancy and SC transition at Tc∼30 K (SC phase). The samples of RbxFe2-ySe2 exhibiting no SC behaviour (non-SC samples) are phase-separated into three phases, The AFM1 phase, another AFM phase with TN2 ∼150 K (AFM2 phase), and a paramagnetic phase with no SC transitions (paramagnetic non-SC phase). In this paper, we present The experimental results of magnetic susceptibility, electrical resistivity, and NMR measurements on single crystals of RbxFe2-ySe2 to reveal physical properties of these co-existing phases in The SC and non-SC samples. The 87Rb and 77Se NMR spectra show that The Fe vacancy concentration is very small in The Fe planes of The SC phase, whereas The AFM2 and paramagnetic non-SC phases in non-SC samples have larger amount of Fe vacancies. The randomness induced by The Fe vacancy in The non-SC samples makes The AFM2 and paramagnetic non-SC phases insulating/semiconducting and magnetically active, resulting in The absence of The superconductivity in RbxFe2-ySe2. © Published under licence by IOP Publishing Ltd.

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