Browsing by Author "Yano, SI"
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- ItemThe cold-neutron triple-axis spectrometer SIKA at OPAL(Australian Institute of Physics, 2018-01-31) Deng, G; Yano, SI; Wu, CM; Peng, JC; Gardner, JS; Imamovic, E; Vorderwisch, P; Li, WH; McIntyre, GJSIKA is a high-flux cold-neutron triple-axis spectrometer funded by Ministry of Science and Technology of Taiwan and currently being operated by National Synchrotron Radiation Research Center. It is located on the OPAL reactor face at the Australian Nuclear Science and Technology Organization (ANSTO). Its incident energy ranges from 2.6meV to 30meV with the highest flux at ~8meV. SIKA is equipped with a multiplexing analyzer consisting of an array of 13 PG crystal blades, a multi-wire detector, a single detector and a diffraction detector. The most frequently-used single-detector mode and the multi-Q constant-Ef mode are demonstrated by using the standard samples, namely, MnF2 and Pb single crystals, respectively. The spin-wave excitation of MnF2, the phonon dispersion of thermoelectric material SeSn, the spin dynamics of the spin-glass system (Ni0.40Mn0.60)TiO3, and other experimental data from SIKA are demonstrated as examples of SIKA’s capabilities and performance. The spin-wave excitation was observed in the quasi-one-dimensional spinladder compound SrCa13Cu24O41, indicating the low background of SIKA. These results indicate that SIKA is a highly-flexible cold triple-axis spectrometer with reasonably low background.
- ItemGapless spin liquid in a square-kagome lattice antiferromagnet(Springer Nature Limited, 2020-06-09) Fujihala, M; Morita, K; Mole, RA; Mitsuda, S; Tohyama, T; Yano, SI; Yu, DH; Sota, S; Kuwai, T; Koda, A; Okabe, H; Lee, H; Itoh, H; Hawai, T; Masuda, T; Sagayama, H; Matsuo, A; Kindo, K; Ohira-Kawamura, S; Nakajima, KObservation of a quantum spin liquid (QSL) state is one of the most important goals in condensed-matter physics, as well as the development of new spintronic devices that support next-generation industries. The QSL in two dimensional quantum spin systems is expected to be due to geometrical magnetic frustration, and thus a kagome-based lattice is the most probable playground for QSL. Here, we report the first experimental results of the QSL state on a square-kagome quantum antiferromagnet, KCu6AlBiO4(SO4)5Cl. Comprehensive experimental studies via magnetic susceptibility, magnetisation, heat capacity, muon spin relaxation (μSR), and inelastic neutron scattering (INS) measurements reveal the formation of a gapless QSL at very low temperatures close to the ground state. The QSL behavior cannot be explained fully by a frustrated Heisenberg model with nearest-neighbor exchange interactions, providing a theoretical challenge to unveil the nature of the QSL state. © 2020 Springer Nature Limited
- ItemNSRRC neutron scattering group at ACNS(Australian Institute of Nuclear Science and Engineering (AINSE), 2018-11-19) Yano, SI; Wang, CW; Peng, H; Wu, CMThe National synchrotron radiation research centre (NSRRC) in Taiwan has a group of scientists stationed at the Australian Centre for Neutron Scattering (ACNS), ANSTO, Australia. Three Instrument Scientists were hired to operate neutron scattering instruments and to serve users; Chun-Min Wu works on Small angle neutron scattering instruments, Chin-wei Wang is a Powder diffractometer scientist and Shinichiro Yano works on the cold triple axis spectrometer SIKA. In addition, one staff member is a software engineer. Under this arrangement, we have built the cold triple axis spectrometer SIKA in the OPAL reactor beam hall at ANSTO. SIKA was designed to study dynamics in magnetic materials in the energy range of meV and below with high resolution. The Taiwan investment adds particular value to the area of materials science whereby Taiwan and Australia both benefit. Following 10 years of construc tion, SIKA has been in the user program since 2015 July with the number of scientific publications growing steadily since then. Taiwanese users now occupy about 20 percent of international proposals submitted to ACNS in the 2018-2 proposal round whilst the Taiwanese neutron scattering community is also growing. We hope for continued good relations between NSRRC and ANSTO with a view to expanding our col laboration. We are currently in the process of hiring an additional instrument scientist who would be working on a reflectometer at ACNS. In this talk, we will present scientific outcomes from the NSRRC neutron group and updates from SIKA. © The Authors.
- ItemSpin dynamics of edge-sharing spin chains in SrCa13Cu24O41(American Physical Society, 2018-11-12) Deng, GC; Yu, DH; Mole, RA; Pomjakushina, E; Conder, K; Kenzelmann, M; Yano, SI; Wang, CW; Rule, KC; Gardner, JS; Luo, HQ; Li, S; Ulrich, C; Imperia, P; Ren, W; Cao, SX; McIntyre, GJThe low-energy magnetic excitation from the highly Ca-doped quasi-one-dimensional magnet SrCa13Cu24O41 was studied in the magnetic ordered state by using inelastic neutron scattering. We observed the gapless spin-wave excitation, dispersive along the a and c axes but nondispersive along the b axis. Such excitations are attributed to the spin wave from the spin-chain sublattice. Model fitting to the experimental data gives the nearest-neighbor interaction Jc as 5.4 meV and the interchain interaction Ja=4.4meV. Jc is antiferromagnetic and its value is close to the nearest-neighbor interactions of the similar edge-sharing spin-chain systems such as CuGeO3. Comparing with the hole-doped spin chains in Sr14Cu24O41, which shows a spin gap due to spin dimers formed around Zhang-Rice singlets, the chains in SrCa13Cu24 O41 show a gapless excitation in this paper. We ascribe such a change from gapped to gapless excitations to holes transferring away from the chain sublattice into the ladder sublattice upon Ca doping. ©2018 American Physical Society
- ItemSpin dynamics of quasi-one-dimensional spin-ladder system SrCa13Cu24O41 in the long-range magnetic ordering state(Australian Institute of Physics, 2018-01-31) Deng, GC; Yu, DH; Mole, RA; Yano, SI; Wang, CW; Rule, KC; Gardner, JS; Luo, H; Li, S; Ulrich, C; Imperia, P; Ren, W; Cao, SX; Pomjakushina, E; Conder, K; Kenzelmann, M; McIntyre, GJSr14-xCaxCu24O41 is a quasi-one-dimensional magnet, which consists of two sublattices: spin ladder and spin chain, forming an incommensurate crystal structure along the c axis, namely, the ladder leg or chain direction. The highly Ca-doped compounds undergo a superconducting phase transition under hydrostatic pressure ~ 3GPa, which is really intriguing since the hole-doped even-leg spin-ladder system was theoretically predicted as superconductors by charge-pairing mechanism through antiferromagnetic interaction on the rungs of spin ladders. In the previous study, we discovered that all compounds with different Ca content have a singlet ground state with a spin-gap ~ 32meV. In the highly Ca-doped sample SrCa13Cu24O41, a long-range magnetic ordering takes place at ~ 4.2K. Interestingly, the singlet spin-liquid state and the long-range magnetic ordering coexist in this compound. In this study, we further investigated its spin dynamics in the ordered phase by using inelastic neutron scattering on PELICAN and SIKA at OPAL. We observed the gapless spin-wave excitation, dispersive along the a and c axes but nondispersive along the b axis, indicating the nature of a 2D magnet. A dynamic model has been proposed to fit the experimental data, indicating three major exchange interactions along rungs (JR), legs (JL) and between neighbor ladders (JInter). This study helps us to understand the origin of the spin liquid ground state in this low-dimensional magnet, in which hole-doping should be attributed to induce the long-range magnetic ordering due to the disorder-induced order effect.
- ItemUnderstanding the structural disorder of (AgxCu1-x)2ZnSnSe4 based kesterite semiconductor by neutron diffraction study(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Quadir, S; Chen, CY; Kuei-Kuan, W; Wang, CW; Wei-Tin, C; Wu, CM; Yano, SI; Chen, KH; Chen, LCThe quaternary semiconductor Cu2ZnSnSe4 (CZTSe) is a promising environment-friendly and low-cost material as a solar cell absorber layer with a power conversion efficiency of 11.6%. Its photovoltaic performance is currently limited due to its disorder between the Copper & Zinc lattice sites, which creates band tailing and creates voltage deficit. By replacing Cu in CZTSe with isovalent Ag, whose ionic radius is larger than that of Cu and Zn, the density of I–II antisite defects could be suppressed. This work has been done to quantify the cation disorders on all cation symmetry sites and the effect of substitution of Ag in the CZTSe crystal structure. (AgxCu1-x)2ZnSnSe4 (A/CZTSe) samples with different compositions were synthesized by a solidstate reaction of the pure element in an evacuated quartz tube. Structural analysis of stoichiometric & offstoichiometric samples were performed using Raman and synchrotron powder diffraction including Rietveld refinement. A neutron diffraction experiment is performed to fully understand the cation distribution analysis in A/CZTSe powder sample as Cu+ and Zn2+ are not distinguishable using conventional X-ray diffraction method due to their isoelectronic character but there is a significant difference in their neutron scattering length (bCu = 7.718 fm, bZn = 5.680 fm). It is found that powder A/CZTSe adopts the kesterite type structure with a partial disorder of copper and zinc on the two Wyckoff position 2c and 2d. Sn has been found on Wyckoff position 2b (0, 0, ½ ), whereas Cu/Zn is located on 2a (0, 0, 0), 2c (0, ½ , 1/4) and 2d (0, ½ , ¾ ) sites. There is a presence of copper vacancies (VCu), various cation anti-site defects (CuZn, ZnCu, ZnSn, and SnZn) have been found for different compositions. This work will also answer the effectiveness of Ag as a substitution of Cu in kesterite based CZTSe, to suppress anti-site disorder. © The authors.