Shin-ichi Shamoto

Superconductivity in Noncentrosymmetric Iridium Silicide Li2IrSi3

The effects of lithium absorption on the crystal structure and electronic properties of IrSi3, a binary silicide with a noncentrosymmetric crystal structure, were studied. X-ray and neutron diffraction experiments revealed that hexagonal IrSi3 (space group P6_3mc) transforms into trigonal Li2IrSi3 (space group P31c) upon lithium absorption. The structure of Li2IrSi3 is found to consist of a planar kagome network of silicon atoms with Li and Ir spaced at unequal distances between the kagome layers, resulting in a polar structure along the c-axis. Li2IrSi3 exhibited type-II superconductivity with a transition temperature Tc of 3.8 K, displaying a structure type that no previous superconductors have been reported to have.

Magnetic Structure and Electromagnetic Properties of LnCrAsO with a ZrCuSiAs-type Structure (Ln = La, Ce, Pr, and Nd)

We report the synthesis, structure, and electromagnetic properties of Cr-based layered oxyarsenides LnCrAsO (Ln = La, Ce, Pr, and Nd) with a ZrCuSiAs-type structure. All LnCrAsO samples showed metallic electronic conduction. Electron doping in LaCrAsO by Mn-substitution for the Cr sites gave rise to a metal-insulator transition. Analysis of powder neutron diffraction data revealed that LaCrAsO had G-type antiferromagnetic (AFM) ordering, i.e., a checkerboard-type AFM ordering in the CrAs plane and antiparallel spin coupling between the adjacent CrAs planes, at 300 K with a large spin moment of 1.57 μB along the c axis. The magnetic susceptibility of LaCrAsO was very small (on the order of 10(-3) emu/mol) and showed a broad hump at ∼550 K. First-principles density functional theory calculations of LaCrAsO explained its crystal structure and metallic nature well, but could not replicate the antiparallel spin coupling between the CrAs layers. The electronic structure of LaCrAsO is discussed with regard to those of related compounds LaFeAsO and LaMnAsO.

Cooperative Order in the Weakly Magnetic Domain of LaFeAsO1−xFx near the Doping Phase Boundary

Spatial phase separation into mesoscopic domains of non-magnetic [superconducting (SC) below Tc ( simeq ) 25.5 K] and two kinds of magnetic phases, one showing disordered spin density wave (d-SDW) order and another associated with glassy weak magnetism (WM), are observed below ∼100 K by muon spin rotation (μSR) in LaFeAsO1−xFx for x = 0.057(3), which is near the boundary of these phases on the doping phase diagram. In contrast to the competing order observed in the regular SDW phase of Ba(Fe1−xCox)2As2, the WM domain exhibits cooperative coupling of superconducting and magnetic order parameters as inferred from strong diamagnetism and the associated negative shift of μSR frequency just below Tc.

Evidence of electronic polarization of the As ion in the superconducting phase of F-doped LaFeAsO

Charge-carrier redistribution invoked by enhanced electronic polarization of the As ion was observed in the superconducting phase of iron arsenide.

Morphology change of multi-walled carbon nanotubes with SiC coating by electron irradiation

The different behaviour between morphology changes of multi-walled carbon nanotube (MWNT) and MWNT with SiC coating was investigated by electron irradiation. High resolution TEM images revealed that deformation of graphitic shells occurred in both MWNT and MWNT with SiC coating by electron irradiation. Electron irradiation began changing the outer and inner diameters of MWNT within 3 minutes exposure, whereas it began changing the diameters of MWNT with SiC coating after 10 minutes exposure. The outer diameter of MWNT increased up to irradiation time of 9 min and then decreased rapidly. On the other hand, the outer diameter of MWNT with SiC coating increased up to irradiation time of 50 min and then was almost saturated. These results lead that the morphology stability of MWNT against electron irradiation can be improved by coating with the SiC layer on MWNT.

Local Structural Analysis by Using Atomic Pair Distribution Function on Mixed Valence Compound LiMn2O4

Katsuaki Kodama1, Naoki Igawa1, Shin-ichi Shamoto1, Kazutaka Ikeda2, Hidetoshi Ohshita2, Naokatsu Kaneko2, Toshiya Otomo2, Kentaro Suzuya3, Akinori Hoshikawa4, and Toru Ishigaki4 1Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan 2Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan 3J-PARC Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan 4 Frontier Research Center for Applied Atomic Sciences, Ibaraki University, Tokai, Ibaraki 319-1106, Japan

Dynamical Spin Susceptibility Studied by Inelastic Neutron Scattering on LaFeAsO1−xFx

Low-energy spin excitations on polycrystalline LaFeAsO1−xFx samples have been studied by inelastic neutron scattering. The Q-integrated dynamical spin susceptibility χ(ω) at 11 meV decreases with increasing fluorine content x across the phase transition from antiferromagnetic to superconducting phases. For superconducting samples, a peak in χ(ω) develops at ω = Eres below Tc, accompanied by its reduction below Eres. Fe 3d orbital contribution on the dynamical spin susceptibility and the electron scattering between Γ and M Fermi surfaces are discussed.

Local Lattice Distortion Caused by Short-range Charge Ordering in Transition Metal Oxides

Katsuaki Kodama1, Naoki Igawa1, Shin-ichi Shamoto1, Kazutaka Ikeda2, Hidetoshi Ohshita2, Naokatsu Kaneko2, Toshiya Otomo2, Kentaro Suzuya3, Akinori Hoshikawa4, and Toru Ishigaki4 1Quantum Beam Science Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan 2Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan 3J-PARC Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan 4 Frontier Research Center for Applied Atomic Sciences, Ibaraki University, Tokai, Ibaraki 319-1106, Japan

2D Neutron Diffraction Imaging on an Ammonite

Materials Science Research Division, Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan Information Technology Systems Management and Operating Office, Center for Computational Science & e-Systems, Tokai, Ibaraki, 319-1195, Japan J-PARC Center, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki, 305-0801, Japan