Browsing by Author "Robinson, RA"
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- ItemThe antiferromagnetic structure of BaPrO3(Australian Institute of Physics, 2004-02-04) Robinson, RA; Goossens, DJ; Telling, MFIn this study, we report the magnetic space group and moment direction in the canted antiferromagnetic system BaPrO3. While previous work had shown that perovskite-based BaPrO3, which is orthorhombic crystallographically, orders antiferromagnetically below 11.7K, and that it also exhibits weak ferromagnetism at the same temperatures, the exact magnetic symmetry and moment directions were previously undetermined. In this report, we show, by means of cold-neutron high-resolution powder diffraction, that the magnetic (Shubnikov) group is in fact Pb’n’m, and that the antiferromagnetism lies along the a-axis, with μx = 0.37±0.03 μB. This is qualitatively and quantitatively consistent with previous neutron diffraction results reporting the configurational symmetry of the antiferromagnetism. Our model explicitly allows for ferromagnetism, and necessarily implies that the ferromagnetism previously observed in bulk magnetisation measurements must lie along the z-axis. We discuss ways in which this prediction might be tested, even in the absence of single crystals of BaPrO3.
- ItemAtomic understanding(CSIRO Publishing, 2009-10) Robinson, RAAs Australia's national nuclear science organisation, ANSTO provides advice and undertakes research on all things nuclear. This can range from advising the Government on uranium mining issues to using nuclear technology to tackle problems in the environment, in health, and in materials science. © 2009, CSIRO Publishing
- ItemCopper diffusion rates and hopping pathways in superionic Cu 2Se: implications for thermoelectricity(SSRN, 2020-10-21) Nazrul Islam, SMK; Mayank, P; Ouyang, Y; Chen, J; Sagotra, AK; Li, M; Cortie, MB; Mole, RA; Cazorla, C; Yu, DH; Wang, XL; Robinson, RA; Cortie, DLThe ultra-low thermal conductivity of Cu2Se is well established, but there is so far no consensus on the underlying mechanism. One proposal is that the fast-ionic diffusion of copper suppresses the acoustic phonons. The diffusion coefficients reported previously, however, differ by two orders of magnitude between the various studies and it remains unclear whether the diffusion is fast enough to impact the heat-bearing phonons. Here, a two-fold approach is used to accurately re-determine the diffusion rates. Ab-initio molecular dynamics simulations, incorporating landmark analysis techniques, were closely compared with experimental quasielastic/inelastic neutron spectroscopy. Reasonable agreement was found between these approaches, consistent with the experimental coefficient of 3.1 ± 1.3 10-5 cm2.s-1 and an activation barrier of 140 ± 60 meV. The hopping mechanism includes short 2 Å hops between tetragonal and interstitial octahedral sites. This process forms dynamic Frenkel defects, however, there is no indication of additional broadening in the density-of-states indicating the intrinsic anharmonic interactions dictate the phonon lifetimes. © Preprint article - 2023 Elsevier Inc.
- ItemCopper diffusion rates and hopping pathways in superionic Cu2Se(Elsevier, 2021-08-15) Nazrul Islam, SMK; Mayank, P; Ouyang, Y; Chen, J; Sagotra, AK; Li, M; Cortie, MB; Mole, RA; Cazorla, C; Yu, DH; Wang, XL; Robinson, RA; Cortie, DLThe ultra-low thermal conductivity of Cu2Se is well established, but so far there is no consensus on the underlying mechanism. One proposal is that the fast-ionic diffusion of copper suppresses the acoustic phonons. The diffusion coefficients reported previously, however, differ by two orders of magnitude between the various studies and it remains unclear whether the diffusion is fast enough to impact the heat-bearing phonons. Here, a two-fold approach is used to accurately re-determine the diffusion rates. Ab-initio molecular dynamics simulations, incorporating landmark analysis techniques, were closely compared with experimental quasielastic/inelastic neutron scattering. Reasonable agreement was found between these approaches, consistent with a diffusion coefficient of 3.1 ± 1.3 x 10−5 cm2.s−1 at 675 K and an activation barrier of 140 ± 60 meV. The hopping mechanism includes short 2 Å hops between tetrahedral and interstitial octahedral sites. This process forms dynamic Frenkel defects. Despite the latter processes, there is no major loss of the phonon mode intensity in the superionic state, and there is no strong correlation between the phonon spectra and the increased diffusion rates. Instead, intrinsic anharmonic phonon interactions appear to dictate the thermal conductivity above and below the superionic transition, and there is only subtle mode broadening associated with the monoclinic-cubic structural transition point, with the phonon density-of-states remaining almost constant at higher temperatures. © 2021 Acta Materialia Inc.
- ItemEvolution of the neutron-scattering capability on the OPAL reactor at ANSTO(Taylor & Francis Online, 2016-04-29) Klose, F; Constantine, P; Kennedy, SJ; Schulz, JC; Robinson, RA; Holden, PJ; McIntyre, GJAustralia is currently in the very privileged position of having the world's newest, fully operating research reactor, OPAL. As a consequence, the suite of neutron-beam instruments is also amongst the youngest and most advanced in the world, with full advantage taken in their construction of lessons learned at reactors elsewhere to develop state-of-the-art instruments that are best suited to the local and regional user communities. There are two thermal-neutron beam ports, two cold-neutron beam ports, and two (future) hot-neutron beam ports around the OPAL reactor core (see Fig. 3 in [1] and [2]). One each of the thermal-neutron and cold-neutron ports feed into a set of three guide bundles that serve the present (first) guide hall. In the initial construction phase, completed in 2007, only the outer two (TG1 and TG3) of the thermal guides, and the outer two (CG1 and CG3) of the cold guides were installed. The other thermal-neutron (TG4) and cold-neutron (CG4) guides are relatively short, to serve single instruments within the reactor beam hall with the highest flux but without eliminating line-of-sight [2]. Table 1 lists the current suite of instruments at the OPAL reactor, with brief technical details and the principal features. Figure 1 shows the layout of the current suite, with the anticipated location of the next instrument, BioRef (vide infra), indicated. We now briefly outline the evolution of the suite. © 2021 Informa UK Limited
- ItemHTS 5 tesla synchrotron and neutron beamline magnets(Institute of Electrical and Electronics Engineers (IEEE), 2009-06) Pooke, DM; Chamritski, V; Fee, M; Gibson, S; King, BT; Tallon, JL; Meissner, M; Feyerherm, R; Olsen, SR; Kennedy, SJ; Robinson, RATwo world-first High-Tc Superconducting (HTS) beamline magnets have been designed, manufactured and commissioned for synchrotron and neutron research facilities. One, for the Hahn-Meitner Institut, is for use with their high-resolution diffraction and resonant magnetic scattering instrument MAGS at the Berlin electron synchrotron facility BESSY. The key features of this 5 tesla split-pair magnet include field performance within a given confined geometry, and low weight. Mounting in a 6-circle goniometer and employing conduction-cooled HTS coils, it operates through 90 degrees of rotation with respect to the beamline axis and scattering plane. The neutron beamline magnet is also a 5 tesla split pair, designed for both neutron reflectometry and small-angle neutron scattering research at the new OPAL neutron facility of the Australian Nuclear Science and Technology Organisation. This much larger magnet offers wide neutron beam accessibility angles in both axial and transverse directions, large (50 mm) sample capability, and mounts on tilt stages operating in two axes. Both magnets use pulse-tube refrigeration for the HTS coils, which have been constructed from high performance BSCCO wire, and both are compatible with separate commercial cryofurnaces providing sample temperatures from 1.5 K (MAGS) or 4 K (OPAL) to over 600 K. © 2009, Institute of Electrical and Electronics Engineers (IEEE)
- ItemInvestigation of field-induced ferromagnetism in Pd-Ni-Fe-P metallic glass by x-ray magnetic circular dichroism(American Institute of Physics, 2009-01-12) Yu, DH; Duriavig, J; Loh, NA; Woodward, RC; Lin, HJ; Chang, FH; Kilcoyne, SH; Stampfl, APJ; Robinson, RAWe have applied x-ray magnetic circular dichroism to investigate the field-induced ferromagnetism in Pd40Ni22.5Fe17.5P20 alloy. The experiment revealed that both Ni and Fe were in a divalent state and that the magnetic properties of the material were determined by the localized 3d electrons of the transition metals. No clear evidence of Ruderman–Kittel–Kasuya–Yosida-type interaction among magnetic clusters was observed. It is believed that the detailed balance of fundamental spin-orbit and exchange interactions as a function of temperature and applied magnetic field determine the different magnetic properties of the alloy. © 2009, American Institute of Physics
- ItemThe neutron beam expansion program at the Bragg Institute(IOP Science, 2014-01-01) Klose, F; Constantine, P; Kennedy, SJ; Robinson, RAThe Bragg Institute is operating the neutron scattering science facilities at the Australian research reactor OPAL. The first set of seven neutron scattering instruments was provided as part of the OPAL construction project which was completed in 2007. During the period 2008 - 2013, the instrument suite was significantly expanded by a further seven instruments. In addition to this, major investments were made to establish a world-class infrastructure for supporting these instruments, including new sample environments, 3He polarisers/analysers, additional neutron guides and a Be filter option for chemical spectroscopy. Creative Commons Attribution 3.0 licence.
- ItemNeutron depolarisation studies on Pd-Ni-Fe-P alloy(The Bragg Institute, Australian Nuclear Science and Technology Organisation, 2005-11-27) Yu, DH; Robinson, RA; Fitzsimmons, MR; Woodward, RC; Gilbert, EPMagnetic metallic glasses have enormous technological importance in, for example, magnetic recording, magnetic refrigeration and the construction of electrical transformers and motors. Traditionally these amorphous materials were prepared by melt spinning to form ribbons. Bulk magnetic metallic glasses based on the quaternary alloy Pd-Ni-Fe-P exhibit interesting phase behaviour depending on temperature and applied magnetic field. For the alloy of Pd40Ni22.5Fe17.5P20, paramagnetic, superparamagnetic, ferromagnetic and spin glass regions are all evidenced (Shen et al. J. Appl. Phys. 85, 4110, (1999)). It is proposed that the complex phase transitions may be due to the frustration caused by competing interactions between magnetic clusters presented in the material. We will present preliminary findings from neutron depolarization studies on the alloy of Pd40Ni22.5Fe17.5P20 as a function of temperature (RT to 10K) and applied magnetic field up to 11T. © The Authors
- ItemNeutron depolarization studies of Pd-Ni-Fe-P alloy(Elsevier, 2007-07-15) Yu, DH; Fitzsimmons, MR; Gilbert, EP; Woodward, RC; Kilcoyne, SH; Robinson, RABulk metallic glasses based on the quaternary alloy Pd-Ni-Fe-P exhibit interesting phase behavior depending on temperature and applied magnetic field. Previous work has suggested that a range of magnetic phases, including paramagnetic, superparamagnetic, ferromagnetic and spin glass, can be observed in this system. We have applied one-dimensional neutron depolarization to explore the correlation of magnetic moments in Pd40M22.5Fe17.5P20 alloy as a function of temperature and applied magnetic field. The results provided evidence for correlation lengths of similar to 200A. The nature of the correlations and the formation mechanism of the induced ferromagnetic phase are discussed. © 2007, Elsevier Ltd.
- ItemNeutron scattering at Australia's replacement research reactor(Australian and New Zealand Institutes of Physics, 2002-01-29) Kennedy, SJ; Robinson, RAAustralia's new research reactor will cater for neutron beam science and radioisotope production from the end of 2005, with unperturbed neutron flux of 4 x 1014 n/cm2/s and at least eight high performance neutron beam instruments. Most of the neutron beam science will be performance in a large fully serviced neutron guide hall. The neutron beam facility will have cold and thermal neutron beams based around supermirror neutron reflecting guides. The design of neutron guides has been optimized to deliver maximum usable neutron flux at neutron scattering instruments located at the reactor face and in the neutron guide hall. The reactor and all the associated infrastructure, with the exception of the neutron beam instruments, is to be built by INVAP S.E. and subcontractors in a turnkey contract. The neutron beam instruments will be developed by ANSTO and other contracted organisations, in consultation with the Australian user community and interested overseas parties. A review of the planned scientific capabilities, a description of the design concepts and key performance issues of the neutron beam facility and a status report on the activities so far will be presented.
- ItemNeutron scattering at Australia's replacement research reactor(Elsevier B. V., 2002-01) Robinson, RA; Kennedy, SJOn August 25 1999, the Australian government gave final approval to build a research reactor to replace the existing HIFAR reactor at Lucas Heights. The replacement reactor, which will commence operation in 2005, will be multipurpose in function, with capabilities for both neutron-beam research and radioisotope production. Regarding beams, cold and thermal neutron sources are to be installed and the intent is to use supermirror guides, with coatings with critical angles up to 3 times that of natural Ni, to transport cold and thermal neutron beams into a large modern guide hall. The reactor and all the associated infrastructure, with the exception of the neutron beam instruments, is to be built by INVAP, SE and subcontractors in a turnkey contract. The goal is to have at least eight leading-edge neutron-beam instruments ready in 2005, and they will be developed by ANSTO and other contracted organisations, in consultation with the Australian user community and interested overseas parties. A review of the planned scientific capabilities, a description of the facility and a status report on the activities so far is given. © 2002 Elsevier Science B.V.
- ItemNovel cryogenic engineering solutions for the new Australian Research Reactor OPAL(American Institute of Physics, 2008-03-16) Olsen, SR; Kennedy, SJ; Kim, S; Schulz, JC; Thiering, R; Gilbert, EP; Lu, W; James, M; Robinson, RAIn August 2006 the new 20MW low enriched uranium research reactor OPAL went critical. The reactor has 3 main functions, radio pharmaceutical production, silicon irradiation and as a neutron source. Commissioning on 7 neutron scattering instruments began in December 2006. Three of these instruments (Small Angle Neutron Scattering, Reflectometer and Time-of-flight Spectrometer) utilize cold neutrons. The OPAL Cold Neutron Source, located inside the reactor, is a 20L liquid deuterium moderated source operating at 20K, 330kPa with a nominal refrigeration capacity of 5 kW and a peak flux at 4.2meV (equivalent to a wavelength of 0.4nm). The Thermosiphon and Moderator Chamber are cooled by helium gas delivered at 19.8K using the Brayton cycle. The helium is compressed by two 250kW compressors (one with a variable frequency drive to lower power consumption). A 5 Tesla BSCCO (2223) horizontal field HTS magnet will be delivered in the 2nd half of 2007 for use on all the cold neutron instruments. The magnet is cooled by a pulse tube cryocooler operating at 20K. The magnet design allows for the neutron beam to pass both axially and transverse to the field. Samples will be mounted in a 4K to 800K Gifford-McMahon (GM) cryofurnace, with the ability to apply a variable electric field in-situ. The magnet is mounted onto a tilt stage. The sample can thus be studied under a wide variety of conditions. A cryogen free 7.4 Tesla Nb-Ti vertical field LTS magnet, commissioned in 2005 will be used on neutron diffraction experiments. It is cooled by a standard GM cryocooler operating at 4.2K. The sample is mounted in a 2nd GM cryocooler (4K–300K) and a variable electric field can be applied. © 2008, American Institute of Physics
- ItemOpportunties for scientific research at Australia's replacement research reactor(Australian Institute of Physics, 2005-03-03) Robinson, RAThe 20-MW Australian Replacement Research Reactor represents possibly the greatest single research infrastructure investment in Australia's history. The project includes a large state-of-the-art liquid deuterium cold-neutron source and supermirror guides feeding a large modern guide hall, in which most of the instruments are placed. Alongside the guide hall, there is good provision of laboratory, office and space for support activities. While the facility has 'space' for up to 18 instruments, the project has funding for an initial set of 8 instruments, which will be ready when the reactor is fully operational in July 2006. Instrument performance will be competitive with the best research-reactor facilities anywhere, and our goal is to be in the top 3 such facilities worldwide.
- ItemPelican - a time of flight cold neutron polarization analysis spectrometer at OPAL(The Physical Society of Japan, 2013-01-01) Yu, DH; Mole, RA; Noakes, TJ; Kennedy, SJ; Robinson, RAPelican, a direct-geometry multi-purpose cold-neutron spectrometer, combines state-of-the-art monochromators and Fermi chopper systems to perform inelastic and quasi-elastic neutron scattering on a variety of materials (powder, polycrystal, single crystal, glass and liquid), covering fields of physics, chemistry and biology. The provision of cryogenic vacuum from sample to detector decreases background to a minimum level. A polarized incident beam is realized by supermirror polarizer and polarization analysis will be achieved by He-3 polarization filter. The instrument is designed to accommodate various sample environments including high magnetic fields, and low and high temperatures. Pelican is the first neutron spectrometer having a moveable high-vacuum Aluminium chamber and a full polarization analysis system. © 2013, Physical Society of Japan.
- ItemPhysics at the Australian Nuclear Science and Technology Organisation(Association of Asia Pacific Societies, 2015-06-01) Robinson, RA; Ionescu, M; Reinhard, MIThe Australian Nuclear Science and Technology Organisation is Australia’s nuclear national laboratory and is the prime repository of nuclear expertise in the country. It plays a key role in research, operation of major facilities,isotope production and advice to Government. It was founded in 1987, as the successor to the Australian Atomic Energy Commission, which had existed from 1952. For almost 50 years, from 1958 until 2006, the AAEC and ANSTO operated the HIFAR heavy-water reactor, the second research reactor to be established in Asia, the first after India. Initially the AAEC’s focus was on nuclear power and nuclear fuel cycle issues, but in the ANSTO era, the focus has shifted towards the technological use of nuclear methods in medicine, the environment and science more generally. © 2015, Association of Asia Pacific Physical Societies.
- ItemProceedings of the international symposium on advanced utilization of research reactors - neutron sources and neutron beam devices(Elsevier B. V., 2001-02-27) Kawai, T; Robinson, RA; Kawaguchi, ANot available.
- ItemA quantum multi-critical point in CeCu6−xAux(Elsevier B. V., 2006-11-15) Robinson, RA; Goossens, DJ; Torikachvili, MS; Kakurai, K; Okumura, HCeCu6−xAux is a well-known heavy-fermion system in which the ground state is antiferromagnetically ordered for x>0.1 and temperatures below 1 K. Non-Fermi liquid behaviour occurs around this critical concentration. The parent compound, CeCu6, exhibits a structural phase transition near 230 K, where it changes from the Pnma orthorhombic room-temperature structure to the P21/c monoclinic structure. The monoclinicity increases as temperature falls, with β reaching 91.44° at 10 K. In the work presented here, powder neutron diffraction is used to explore the monoclinicity at 8 K as a function of composition for 0.00.1, indicates that long-range order disappears at exactly the same critical concentration. At a minimum, the structural distortion and antiferromagnetism seem to be competing with each other, and this raises the intriguing possibility that lattice degrees of freedom are important in the non-Fermi liquid regime.
- ItemScientific opportunities at OPAL, the Australian replacement research reactor(International Group On Research Reactors, 2005-09-12) Robinson, RANot available
- ItemScientific opportunities at OPAL, the new Australian research reactor(American Physical Society, 2007-03-06) Robinson, RAAustralian physics is entering a new ``golden age,'' with the startup of bright new neutron and photon sources in Sydney and Melbourne, in 2006 and 2007 respectively. The OPAL reactor and the Australian Synchrotron can be considered the greatest single investment in scientific infrastructure in Australia's history. They will essentially be ``sister'' facilities, with a common open user ethos, and a vision to play a major role in international science. Fuel was loaded into the reactor in August 2006, and full power (20MW) achieved in November 2006. It is our plan to commence the formal user program in mid 2007, but commissioning experiments will have taken place well before then. The first three instruments in operation will be a high-resolution powder diffractometer (for materials discovery), single-crystal diffractometer (for small-molecule crystallography) and a strain scanner (for mechanical engineering and industrial applications). These will be closely followed by four more instruments with broad application in nanoscience, condensed- matter physics and other scientific disciplines. Instrument performance will be competitive with the best research-reactor facilities anywhere. To date there is committed funding for 9 instruments, with a capacity to install a total of ∼18 beamlines. An update will be given on the status of OPAL, its thermal and cold neutron sources, its instruments and hopefully the first data.