Comprehensive Research Organization for Science and Society

Ibaraki, Japan

Comprehensive Research Organization for Science and Society

Ibaraki, Japan
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Suzuki T.T.,Japan National Institute of Materials Science | Sakai O.,Japan National Institute of Materials Science | Sakai O.,Comprehensive Research Organization for Science and Society
Physical Review B | Year: 2017

Surface magnetism is analyzed by spin-dependent He+-ion neutralization (the Auger neutralization) in the vicinity of a surface using an electron spin-polarized low-energy He+-ion beam [spin-polarized ion scattering spectroscopy (SP-ISS)]. Recently, spin-orbit coupling (SOC) has been found to act as another mechanism of spin-dependent low-energy He+-ion scattering. Thus, it is crucial for surface magnetism analyses by SP-ISS to separate those two mechanisms. In the present study, we investigated the spin-induced asymmetry in scattering of low-energy He+ ions on ultrathin Au and Sn films as well as the oxygen adsorbate on a magnetized-Fe(100) surface where these two mechanisms may coexist. We found that the Fe surface magnetism immediately disappeared with the growth of those overlayers. On the other hand, we observed no induced spin polarization in the Au and Sn thin films even in the very initial stage of the growth. We also observed that the spin asymmetry of the O adsorbate was induced by the magnetism of the underlying Fe substrate. The present study demonstrates that the two mechanisms of the spin-asymmetric He+-ion scattering (the ion neutralization and SOC) can be separated by an azimuthal-angle-resolved SP-ISS measurement. © 2017 American Physical Society.

Sakai O.,Comprehensive Research Organization for Science and Society | Sakai O.,Japan National Institute of Materials Science | Suzuki T.T.,Japan National Institute of Materials Science
Journal of the Physical Society of Japan | Year: 2017

The scattering of the electron-spin-polarized 4He+ beam on paramagnetic materials has an anomalously large asymmetric scattering component (ASC) around 5%, which is 104 of that expected from the spin-orbit coupling (SOC) for the potential of the target nucleus. In addition, the ASC of some materials (for example, Au and Pt) changes sign near the scattering angle (θ) of 90° unlike the result predicted by using the potential scattering theory. When the 4He+ approaches the target, virtual electron-transfer (ET) excitations between them occur. The effects of the SOC of electrons (SOEs) on the target atom in the ET intermediate state are studied within the frame of the lowest-order perturbation theory about the ET process. The ASC is caused through the combination of the quantum development of electron orbital states under the SOEs and the He nucleus motion in the intermediate state because the preferred orbital states for the ET depend on the position of the He nucleus. It is shown by a numerical calculation that the present process has the possibility of producing the ASC with a magnitude of around 0.1. In the present process, the ASC shows a θ dependence of cos θ sin θ, which changes sign at θ = 90° when the excited orbital in the ET state has the d-character like the Au and Pt cases. © 2017 The Physical Society of Japan.

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.

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 | 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.

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