Browsing by Author "Vorderwisch, P"

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    The 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, GJ
    SIKA 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.
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    The cold-neutron triple-axis spectrometer SIKA at OPAL
    (International Conference on Neutron Scattering, 2017-07-12) Deng, G; Yano, S; Wu, CM; Peng, JC; Imamovic, E; Vorderwisch, P; Li, WH; Gardner, JS
    SIKA is a high-flux cold-neutron triple-axis spectrometer built on the cold source CG4 of the 20MW Open Pool Australian Light-water (OPAL) reactor at Australian Nuclear Science and Technology Organization (ANSTO) by Taiwan.[1] As a state-of-the-art triple-axis spectrometer, SIKA is equipped with a large double-focusing pyrolytic graphite (PG) monochromator, a multiblade PG analyser and a multi-detector system. The design, functions, and capabilities of SIKA are presented. The spin wave excitation of MnF2, the phonon dispersion of thermoelectric material SeSn,[2] the spin dynamics of spin glass system (Ni0.40Mn0.60)TiO3[3] and other experimental data from SIKA are demonstrated as examples of SIKA’s capabilities and performance.
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    Observation of phasons in the magnetic shape memory alloy Ni2MnGa
    (IOP Sciences, 2007-03) Shapiro, SM; Vorderwisch, P; Habicht, K; Hradil, K; Schneider, H
    An inelastic neutron scattering study of the lattice dynamics of the martensite phase of the ferromagnetic shape memory alloy, Ni2MnGa, reveals the presence of well-defined phasons associated with the charge density wave (CDW) resulting from Fermi surface (FS) nesting. The velocity and the temperature dependence of the phason are measured as well as the anomalous [110]-TA(2) phonon. © 2007, EPLA
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    Phason mode in the incommensurate martensitic phase of Ni2MnGa - observed by neutron spectroscopy
    (Australian Institute of Physics, 2006-12-04) Vorderwisch, P; Shapiro, SM; Habicht, K; Hradil, K; Schneider, H
    The ferromagnetic shape-memory alloy Ni2MnGa, of technological interest as a magnetically driven actuator, undergoes a martensitic transformation from a cubic austenite to a tetragonally distorted martensite structure. Previous inelastic neutron scattering experiments, performed in the martensite phase, show an anomaly in the phonon dispersion for the [110] transverse acoustic branch TA2 [1]. This anomaly is identified (in ab-initio calculations through examination of Fermi-surface nesting and electron-phonon coupling) as a Kohn anomaly [2] and occurs at a wave vector incommensurate with the underlying lattice. Elastic neutron scattering reveals a modulation of the martensite phase with this incommensurate wave vector [1]. In very recent inelastic experiments, performed with cold- and thermal-neutron triple-axis-spectrometers, in addition to the known acoustic branch a new dispersive branch was found, showing all characteristics of a phason mode. In our interpretation, the new mode is caused by a charge-density-wave in the incommensurately distorted lattice. Inelastic neutron scattering is the only technique able to unambiguously detect a phason branch - and successful examples are rare. [1] P. Vorderwisch and S.M. Shapiro, submitted [2] C. Bungaro et al., Phys. Rev. B 68 (2003) 134104
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    SIKA - a new triple-axis-spectrometer for cold neutrons
    (Australian Institute of Physics, 2006-12-05) Li, WH; Yang, CC; Vorderwisch, P
    The new OPAL reactor at ANSTO will be among the world-top research reactors equipped with a cold neutron source. A cold-neutron triple-axis-spectrometer named SIKA, designed and to be operated by a research team from Taiwan, will extend the day-one instrumentation at OPAL especially for measurements of low-energy excitations in single crystals (phonon or magnon dispersion relations) or, in an elastic mode, of weak superstructure reflections. Modern applications of such a spectrometer are magnetic-field driven quantum-phase transitions and magnetic-field induced ordering phenomena in high TC superconductors. Whereas a high resolution of such a spectrometer is inherently given by the use of cold neutrons, a high intensity of measured signals will be obtained using focusing methods. An option to work with polarised neutrons will also be available. We describe the conceptual design of SIKA and its expected performance, both based on MonteCarlo simulations using the codes McStas and MCNP. Finally we compare SIKA with other state-of-the-art cold-neutron triple-axis-spectrometers.
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    SIKA - the cold-neutron triple-axis spectrometer with multiplexing analyzer at Bragg Institute
    (Asia - Oceania Neutron Scattering Association, 2015-07-19) Deng, GC; McIntyre, GJ; Wu, CM; Gardner, JS; Vorderwisch, P; Li, WH
    SIKA 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 locates at the OPAL reactor face at the Australian Nuclear Science and Technology Organisation (ANSTO). Its incident energy ranges from 2.5meV to 30meV with the highest flux at ~8meV. With an advanced design, SIKA is equipped with an analyzer array of 13 PG(002) blades (Fig. 1), a multi-wire detector, and a separate diffraction detector. Such a design allows SIKA to run in a traditional step-by-step mode or in various mapping (or dispersive) modes by changing the configuration of analyzers and detectors. Several typical mapping modes are analyzed and simulated using Monte Carlo ray-tracing package SIMRES of RESTRAX. [1] The performance of different mapping modes are demonstrated and evaluated, providing the dispersion relations of these operation modes as references for experimental studies. In hotcommissioning, a multiplexing mode with constant Ef was used to measure the phonon dispersion in a Pb single crystal. The simulation and experiment results demonstrate the flexibility and fast data-collecting potential of SIKA as a next generation cold neutron triple-axis spectrometer.
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    Simulation of energy dispersive mode for RITA-type cold neutron triple axis spectrometer SIKA
    (Australian Institute of Physics, 2012-02-02) Deng, GC; Vorderwisch, P; Wu, CM; McIntyre, GJ; Li, WH
    SIKA, a high flux cold triple axis spectrometer at OPAL reactor, is equipped with a 13-blade analyser and position sensitive detector. This multiplexing design endows SIKA with high flexibility to run in either traditional or dispersive modes. In this study, the energy dispersive mode for two different energy transfers is simulated using the Monte Carlo ray-trace package SIMRES. The results show that SIKA could work effectively in this mode at low and intermediate energy transfers with reasonable energy and Q resolution. The simulated energy resolution is about 0.23 meV for an energy transfer of ħω = 5 meV and increases to 1.8 meV for ħω = 15 meV. This work provides a valuable reference for future inelastic neutron scattering experiments on SIKA.
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    Simulation of multiple operation modes for the cold neutron triple axis spectrometer SIKA at Bragg Institute
    (Australian Institute of Physics, 2012-02-02) Deng, GC; Vorderwisch, P; Wu, CM; McIntyre, GJ; Li, WH
    The coming high flux cold-neutron triple axis spectrometer, SIKA at Bragg Institute, is built with an unconventional design, equipped with a multi-strip analyzer array of 13 PG(002) blades (see Fig. 1), a linear position-sensitive detector and a separate diffraction detector. Such a design allows SIKA to run in a traditional step-by-step mode or various mapping (or dispersive) modes by changing the configuration of analyzers and detectors. In this study, several typical mapping modes are analyzed and simulated using Monte Carlo ray-trace package SIMRES of RESTRAX. [1] The performance of different mapping modes are demonstrated and evaluated, providing the dispersion relations of these operation modes as references for experimental studies. The simulation shows the flexibility and fast data collecting potential of SIKA as a new generation of triple axis spectrometer. The simulated data could be compared with the experimental data in the future and as a reference to the selection of effective operation modes.