Browsing by Author "Allen, J"

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    Comparing inelastic neutron scattering with theory to understand the complex magnetic interactions in a low-dimensional frustrated magnet
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Allen, J; Rule, KC; Mole, RA; Heinze, L; Süllow, S
    Frustrated magnetic systems have gained a lot of recent interest as they can exhibit exotic magnetic quantum states such as spin-liquid and spin-nematic states [1,2]. The natural mineral atacamite, Cu2Cl(OH)3, is one such material which has been reported to exhibit magnetic behaviour characteristic of a frustrated quantum magnet [3]. It also shares structural similarity with another cuprate, herbertsmithite, whose kagomé lattice is predicted to host a spin liquid ground state [4]. Little is understood about the magnetic properties of the natural orthorhombic structure of atacamite in contrast to its other structural polymorphs. This work studies this lesser understood orthorhombic atacamite, where Cu2+ ions form a pyrochlore lattice. The novel magnetic interactions and quantum states in materials like atacamite lends itself to spintronic applications where understanding spin interactions can unveil opportunities for intentionally manipulating these spins. Time-of-flight inelastic neutron scattering measurements on single crystalline atacamite have been performed at Pelican with an incident wavelength of 4.69Å. Excitations were observed at 1.5K, and weakened as temperature was increased beyond the antiferromagnetic transition temperature of TN = 9.0K [5] to 20K. The strongest dispersion was found along the H00 direction with two nested modes observed up to an energy transfer of 3meV. Relatively weak dispersion was seen along 00L, and a flat mode was observed in out-of-plane scattering covering a narrow section in 0K0. Ab initio band structure calculations have indicated a 1D sawtooth chain model for the dominant magnetic exchange paths in atacamite [6]. This chain model can be consolidated with our neutron scattering measurements and SpinW calculations. However, the relative magnitudes and directions of the predicted exchange couplings indicate the strongest interactions to be along 0K0, and this does not agree with the strongest dispersion measured experimentally in the H00 direction at zero field. To better understand the interactions in atacamite, in-field time-of-flight measurements have also been conducted in magnetic fields up to 6.5T, applied along the crystallographic b-axis. Data were collected using Pelican and the new open geometry, fully compensated, 7T vertical magnet. We will present the results of these inelastic neutron scattering measurements along with corresponding SpinW calculations to address the inconsistencies between theory and data when considering the exchange interactions in atacamite.
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    Few-layer hexagonal boron nitride / 3D printable polyurethane composite for neutron radiation shielding applications
    (Elsevier, 2023-03) Knott, JC; Khakbaz, HS; Allen, J; Wu, L; Mole, RA; Baldwin, C; Nelson, A; Sokolova, AV; Beirne, S; Innis, PC; Frost, DG; Cortie, DL; Rule, KC
    Functional polymer composites can confer a range of benefits in practical applications that go beyond the individual properties of the constituent materials. Here we investigate and characterize the neutron absorbing capability of few-layer hexagonal boron nitride (h-BN) in composite with a 3D-printable thermoplastic polyurethane, and present experiment and simulation data to understand the processes and mechanisms in play. Shielding and protection from neutrons can be necessary in a range of terrestrial and space-based applications. The neutron absorption of composites with varying fractions of h-BN is strongly energy-dependent in the low-energy regime below 10 meV, and a composite containing 20 wt% h-BN shows a 70-fold reduction in the transmission relative to pure polyurethane at 0.5 meV neutron energies. This is attributed to the strong neutron capture cross-section of the naturally abundant boron-10 isotope, with energy-dependent measurements up to 100 meV confirming this point. Using inelastic neutron spectroscopy, we identify additional effects from the hydrogen in the polyurethane which both scatters diffusively and moderates neutrons inelastically via its phonon spectrum, enhancing the neutron absorption characteristics. Two models – based on analytic functions and Monte Carlo numerical techniques – are presented, and show excellent agreement with experiment results. The 3D-printability of the composite is demonstrated, and the opportunities and challenges for deploying these composites in neutron radiation protection applications are discussed. © 2022 Published by Elsevier Ltd.
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    One layer at a time: unlocking novel materials and structures for neutron radiation environments through additive manufacturing
    (Australian Nuclear Science and Technology Organisation, 2021-11-26) Knott, J; Rule, KC; Cortie, DL; Innis, P; Baldwin, C; Beirne, S; Allen, J
    The UOW-ANSTO Seed Funding program is an initiative aimed at encouraging new collaborations between researchers at the University of Wollongong and ANSTO - bringing together teams with diverse and complementary skillsets to tackle questions that require multi-disciplinary approaches. In 2019, a team of researchers from ANSTO’s Australian Centre for Neutron Scattering (ACNS), UOW’s Australian Institute for Innovative Materials (AIIM) and the Translational Research Initiative for Cell Engineering and Printing (TRICEP) came together to tackle the question “Can the structures and materials made possible by additive manufacturing enable novel solutions for neutron radiation environments?” To explore this question, we undertook activities in three themes: • THEME 1 – Polymers for neutron shielding and collimation • THEME 2 – Low-hydrogen polymers for neutron sample environments • THEME 3 – Metals and alloys for neutron sample environments This presentation will discuss activities undertaken in these themes, including: • THEME 1: investigating novel boron nitride/polyurethane materials developed by the UOW for use in neutron shielding and collimation applications via experiments on the Taipan, Pelican, Bilby and Platypus facilities at ANSTO; • THEME 2: the development of a custom low-hydrogen polymer (FEP) printing apparatus and optimised print procedure, to our knowledge one of the first such facilities. This has resulted in the production of low-hydrogen sample holders for use in ANSTO neutron environments; and • THEME 3: leveraging the world-class facilities and expertise in metal additive manufacturing at TRICEP to produce ‘sample can’ components in titanium and aluminium for validation and as a platform for future customised sample environment devices. This presentation will also discuss possibilities and future plans for work in this exciting area. © 2021 The Authors
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    ‘One layer at a time’: unlocking novel materials and structures for neutron radiation environments through additive manufacturing
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Allen, J; Baldwin, C; Khakbax, H; Beirne, S; Filippi, B; Innis, P; White, R; Wu, L; Cortie, DL; Rule, KC; Knott, J
    The fact that neutrons can penetrate deeply makes them an excellent tool for probing the inner structures of materials, however this property also means that effective management of neutron radiation is a central challenge in nuclear engineering, neutron beam science and in the electronics industry. Neutrons also form a significant proportion of space radiation, and therefore novel, lightweight materials and structures for space radiation shielding are at the forefront of Australian and international space science development. Additive Manufacturing provides opportunities for creating novel structures with often complex geometries – and in materials not otherwise possible with traditional manufacturing techniques. We have brought together a team through the ANSTO-UOW Seed Funding Scheme to focus on the question: “Can the structures and materials made possible by additive manufacturing enable novel solutions for neutron radiation environments?” THEME 1 – Polymers for neutron shielding and collimation: particularly focusing on boron nitride/polymer composites and the possibilities these composites, coupled with 3D printing techniques, can open for neutron shielding and collimation applications – both terrestrial- and space-based THEME 2 – Low-hydrogen polymers for neutron sample environments: focusing on 3D-printable polymers for additive manufacturing low-background components for neutron sample environments THEME 3 – Metals and alloys for neutron sample environments: investigating additive manufacturing of metals – particularly aluminium – and alloys for neutron environment components. This presentation discusses the opportunities and some of the promising approaches for neutron environment additive manufacturing and novel composite materials – with specific examples and initial results from this collaborative endeavour.
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    Verification of L-alanine single-crystallinity for anisotropic synchrotron terahertz measurements
    (Australian Nuclear Science and Technology Organisation, 2021-11-25) Allen, J; Sanders, T; Horvat, J; Rule, KC; Lewis, RA
    One way to probe the molecular interactions of a material is by using terahertz (THz) spectroscopy, which has been used to study L-alanine in detail [1]. However, isotropic THz spectroscopy has limitations in identifying the origin of vibrational modes since the direction of the associated dipole moment is random in an isotropic THz measurement. Therefore, there is a benefit to performing anisotropic (polarised) THz measurements. This work represents the first anisotropic measurements performed on L-alanine, the simplest chiral amino acid, and one of the earliest amino acids fundamental to early life on Earth [2]. An appropriate sample for anisotropic measurements must be highly single-crystalline. This presentation describes a method to prepare and test a sample for anisotropic THz measurements. Samples have been grown at the University of Wollongong, and sample verification has been done at ACNS’s Taipan triple-axis spectrometer. Using Taipan, a narrow mosaic spread of ~0.8° was determined, and single, well-fitted Gaussian peaks were observed in both sample rotation and Q-space scans, suggesting high single-crystallinity in our L-alanine samples. Additionally, the Taipan measurements were able to verify the orientation of the L-alanine single crystals with respect to their crystallographic axes. Anisotropic THz measurements were taken on the THz – Far Infrared beamline at the Australian Synchrotron using a wire-grid polariser. Distinct absorption bands were observed for different crystal orientations, further confirming single-crystallinity, and identifying the dipole moment directions for the observed modes. We thus demonstrate a method of performing anisotropic THz measurements. © 2021 The Authors