Watanabe T.,Nihon University |
Takita S.,Nihon University |
Tomiyasu K.,Tohoku University |
Kamazawa K.,Comprehensive Research Organization for Science and Society
Physical Review B - Condensed Matter and Materials Physics | Year: 2015
Ultrasound velocity measurements were performed on a single crystal of spin-frustrated ferrite spinel ZnFe2O4 from 300 K down to 2 K. In this cubic crystal, all the symmetrically independent elastic moduli exhibit softening with a characteristic minimum with decreasing temperature below ∼100 K. This elastic anomaly suggests a coupling between dynamical lattice deformations and molecular-spin excitations. In contrast, the elastic anomalies, normally driven by the magnetostructural phase transition and its precursor, are absent in ZnFe2O4, suggesting that the spin-lattice coupling cannot play a role in relieving frustration within this compound. The present study infers that, for ZnFe2O4, the dynamical molecular-spin state evolves at low temperatures without undergoing precursor spin-lattice fluctuations and spin-lattice ordering. It is expected that ZnFe2O4 provides the unique dynamical spin-lattice liquidlike system, where not only the spin molecules but also the cubic lattice fluctuate spatially and temporally. © 2015 American Physical Society.
Komatsu K.,University of Tokyo |
Munakata K.,Comprehensive Research Organization for Science and Society |
Matsubayashi K.,University of Tokyo |
Uwatoko Y.,University of Tokyo |
And 3 more authors.
High Pressure Research | Year: 2015
Zirconium-based bulk metallic glass (Zr-based BMG) has outstanding properties as a cylinder material for piston-cylinder high pressure apparatuses and is especially useful for neutron scattering. The piston-cylinder consisting of a Zr-based BMG cylinder with outer/inner diameters of 8.8/2.5mm sustains pressures up to 1.81GPa and ruptured at 2.0GPa, with pressure values determined by the superconducting temperature of lead. The neutron attenuation of Zr-based BMG is similar to that of TiZr null-scattering alloy and more transparent than that of CuBe alloy. No contamination of sharp Bragg reflections is observed in the neutron diffraction pattern for Zr-based BMG. The magnetic susceptibility of Zr-based BMG is similar to that of CuBe alloy; this leads to a potential application for measurements of magnetic properties under pressure. © 2015 Taylor & Francis.
Komiyama H.,Tokyo Institute of Technology |
Sakai R.,Tokyo Institute of Technology |
Hadano S.,Tokyo Institute of Technology |
Hadano S.,Kochi University |
And 10 more authors.
Macromolecules | Year: 2014
A series of amphiphilic liquid crystalline diblock copolymers, PEO m-b-PMA(Az)n, consisting of hydrophilic poly(ethylene oxide) and hydrophobic poly(methacrylate) moieties with side chains containing liquid crystalline (LC) azobenzene moieties, produced highly ordered microphase-separated films with PEO cylinders aligned perpendicular to the smectic LC layer of azobenzene in the PMA(Az) matrix. In this paper, morphological phase diagrams of PEOm-b-PMA(Az)n diblock copolymers above and below the isotropic transition temperature of LC azobenzene (Tiso) are presented. The diagrams are based on small-angle X-ray scattering (SAXS) measurements of approximately 70 kinds of polymers with varying degrees of polymerization in each block. An asymmetric phase diagram described against the volume fraction of PEO (fPEO) was obtained at temperatures above and below Tiso. The lamellar phase appears in the fPEO window 0.52 ≤ fPEO ≤ 0.78 above and below Tiso. Besides, the wide window, 0.087 ≤ fPEO < 0.52, allows the PEO cylinder phase to form below Tiso. In particular, the PEO sphere phase, observed above Tiso, was completely eliminated through an order-order transition (OOT) to the PEO cylinder phase in the window 0.087 ≤ fPEO ≤ 0.23. Such a large expansion in the PEO-cylinder-phase window could be attributed to the main chain of LC PMA(Az) being shorter than that of the flexible PEO chain, and LC azobenzene forming a smectic layer in the microphase separated system. © 2014 American Chemical Society.
Sugiyama J.,Toyota Central Research and Development Laboratories Inc. |
Mukai K.,Toyota Central Research and Development Laboratories Inc. |
Nozaki H.,Toyota Central Research and Development Laboratories Inc. |
Harada M.,Toyota Central Research and Development Laboratories Inc. |
And 5 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013
In order to elucidate the antiferromagnetic (AF) spin structure below TN∼35 K and to clarify the diffusive behavior of Li+ ions in the layered compound Li2MnO3, we have performed a muon-spin rotation and relaxation (μ+SR) experiment using a powder sample in the temperature range between 2 and 500 K. Below TN, the zero-field (ZF-) μ+SR spectrum showed a clear oscillation that consists of two muon-spin precession signals with different frequencies. Combining with the dipole field calculations, it was found that the most probable spin structure for Li2MnO3 is the C x-type AF order in which Mn moments align parallel or antiparallel to the a axis in the [Li1/3Mn2/3]O2 layer, and a ferromagnetic chain along the a axis aligns antiferromagnetically along both the b and c axes. The ordered Mn moment was estimated as 2.62μB at 2 K. In the paramagnetic state, ZF- and longitudinal-field μ+SR spectra exhibited a dynamic nuclear field relaxation. From the temperature dependence of the field distribution width, the Li+ ions were found to diffuse mainly along the c axis through the Li ion in the [Li 1/3Mn2/3]O2 layer. Also, based on the field fluctuation rate, a self-diffusion coefficient of Li+ ions (D Li) at 300 K was estimated as 4.7(4)×10-11 cm2/s with the thermal activation energy Ea=0.156(3) eV. © 2013 American Physical Society.
Machida S.,Comprehensive Research Organization for Science and Society
Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu | Year: 2016
The diamond anvil cells (DACs) for the neutron diffraction experiments were developed at the high-pressure diffraction instrument, the Spallation Neutrons and Pressure (SNAP) in the Spallation Neutron Source (SNS), Oak Ridge National Laboratory, USA. In the SNAP, the neutron data of ice VII were collected up to 94 GPa at room temperature. Also, the low temperature neutron experiments can be performed by using the DAC, PE-cell and gas-pressure-cell. In this article, the introduction for experimental techniques and review of the high-pressure neutron experiments on icy materials are shown. © 2016, Japan Society of High Pressure Science and Technology. All rights reserved.
Jin X.,High Energy Accelerator Research Organization |
Nakamoto T.,High Energy Accelerator Research Organization |
Ito T.,Japan Atomic Energy Agency |
Ito T.,Comprehensive Research Organization for Science and Society |
And 7 more authors.
Superconductor Science and Technology | Year: 2012
We prepared three types of non-Cu RHQ-Nb 3Al wire sample with different matrix structures: an all-Ta matrix, a composite matrix of Nb and Ta with a Ta inter-filament, and an all-Nb matrix. Neutron diffraction patterns of the wire samples were measured at room temperature in the J-PARC TAKUMI. To obtain the residual strains of the materials, we estimated the lattice constant a by multi-peak analysis in the wires. A powder sample of each wire was measured, where the powder was considered to be strain free. The grain size of all the powder samples was below 0.02mm. For the wire sample with the all-Nb matrix, we also obtained the lattice spacing d by a single-peak analysis. The residual strains of the Nb 3Al filament were estimated from the two analysis results and were compared. The resulting residual strains obtained from the multi-peak analysis showed a good accuracy with small standard deviation. The multi-peak analysis results for the residual strains of the Nb 3Al filaments in the three samples (without Cu plating) were all tensile residual strain in the axial direction, of 0.12%, 0.12%, and 0.05% for the all-Ta matrix, the composite matrix, and the all-Nb matrix, respectively. The difference in the residual strain of the Nb 3Al filament between the composite and all-Nb matrix samples indicates that the type of inter-filament material shows a great effect on the residual strain. In this paper, we report the method of measurement, method of analysis, and results for the residual strain in the three types of non-Cu RHQ-Nb 3Al wires. © 2012 IOP Publishing Ltd.
PubMed | Japan Atomic Energy Agency, Comprehensive Research Organization for Science and Society, Oak Ridge National Laboratory, Kyoto University and High Energy Accelerator Research Organization
Type: Journal Article | Journal: The journal of physical chemistry. B | Year: 2016
The detailed structure of a nanogel formed by self-association of cholesterol-bearing pullulans (CHPs) was determined by contrast variation small-angle neutron scattering. The decomposition of scattering intensities into partial scattering functions of each CHP nanogel component, i.e., pullulan, cholesterol, and the cross-term between the pullulan and the cholesterol, allows us to investigate the internal structure of the nanogel. The effective spherical radius of the skeleton formed by pullulan chains was found to be 8.1 0.3 nm. In the CHP nanogel, there are about 19 cross-linking points where a cross-linking point is formed by aggregation of trimer cholesterol molecules, and the spatially inhomogeneous distribution of the cross-linking points in the nanogel can be represented by the mass fractal dimension of 2.6. The average radius of gyration of the partial chains can also be determined to be 1.7 0.1 nm by analyzing the extracted cross-correlation between the cross-linker and the tethered polymer chain quantitatively, and the size agrees with the value assuming random distribution of the cross-linkers on the chains. As the result, the complex structure of the nanogels is coherently revealed at the nanoscopic level.
PubMed | Japan Atomic Energy Agency, Comprehensive Research Organization for Science and Society and University of Tokyo
Type: Journal Article | Journal: Acta crystallographica Section B, Structural science, crystal engineering and materials | Year: 2015
Magnesium dichloride decahydrate (MgCl210H2O) and its deuterated counterpart (MgCl210D2O) are identified for the first time by in-situ powder synchrotron X-ray and spallation neutron diffraction. These substances are crystallized from a previously unidentified nanocrystalline compound, which originates from an amorphous state at low temperature. A combination of a recently developed autoindexing procedure and the charge-flipping method reveals that the crystal structure of MgCl210H2O consists of an ABCABC sequence of Mg(H2O)6 octahedra. The Cl(-) anions and remaining water molecules unconnected to the Mg(2+) cations bind the octahedra, similar to other water-rich magnesium dichloride hydrates. The D positions in MgCl210D2O, determined by the difference Fourier methods using the neutron powder diffraction patterns at 2.5GPa, show the features such as bifurcated hydrogen bonds and tetrahedrally coordinated O atoms, which were not found in other forms of magnesium chloride hydrates.
PubMed | Toyohashi University of Technology, Comprehensive Research Organization for Science and Society, Kyushu University, Australian Nuclear Science and Technology Organisation and 2 more.
Type: Journal Article | Journal: Journal of applied crystallography | Year: 2016
Pulsed neutron sources enable the simultaneous measurement of small-angle neutron scattering (SANS) and Bragg edge transmission. This simultaneous measurement is useful for microstructural characterization in steel. Since most steels are ferromagnetic, magnetic scattering contributions should be considered in both SANS and Bragg edge transmission analyses. An expression for the magnetic scattering contribution to Bragg edge transmission analysis has been derived. The analysis using this expression was applied to Cu steel. The ferrite crystallite size estimated from this Bragg edge transmission analysis with the magnetic scattering contribution was larger than that estimated using conventional expressions. This result indicates that magnetic scattering has to be taken into account for quantitative Bragg edge transmission analysis. In the SANS analysis, the ratio of magnetic to nuclear scattering contributions revealed that the precipitates consist of body-centered cubic Cu
News Article | October 26, 2015
In a study published in Nature Communications, scientists from the RIKEN Center for Emergent Matter Science in Japan have found a way to manipulate skyrmions – tiny nanometer-sized magnetic vortices found at the surface of magnetic materials – using mechanical energy. Skyrmions have been widely touted as providing the basis for new high-density memory devices because of their small size and relative stability. However, it has proven difficult to create, delete and move them, and so skyrmion-based devices are not yet competitive with other next-generation memory devices based on electron spin. According to Yoichi Nii of the Emergent Device Research Team, the first author of the study: "We began from the simple question of whether it would be practical to turn skyrmions on and off with mechanical force, and wondered how much force would be required. We imagined it would be substantial." The group set out to answer this question using a specially-designed stress probe that could apply mechanical stress to the surface of manganese silicide, a ‘chiral magnetic’ known to host skyrmions, cooled to very low temperatures. They found, to their surprise, that the force required to create and delete skyrmions was quite low, less than ten nanonewtons per skyrmion, comparable to the pressure exerted by the tip of a conventional pencil when writing in a notebook. A force applied perpendicular to the magnetic field led to the creation of skyrmions, while a force applied parallel to the field deleted the skyrmions, making it possible to turn them on and off mechanically. “This means,” says Yoshihiro Iwasa, leader of the Emergent Device Research Team, “that we may be able to fabricate devices in which skyrmions are created and deleted by a small mechanical force. This could be an inexpensive and low-energy-consuming way to create new low-cost memory devices and open the road to skymionics.” One drawback of the current approach is that it requires cooling the magnet to very low temperatures for the system to work. According to Nii, they plan to continue experiments with a variety of materials to try to identify ones that host skyrmions that can be manipulated mechanically at higher temperatures. The work was done in collaboration with the University of Tokyo, the Japan Proton Accelerator Research Complex and the Comprehensive Research Organization for Science and Society. This story is adapted from material from RIKEN, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.