Browsing by Author "Lee, WT"
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- ItemCanted magnetism in modulated thin-film superlattices Oliver(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Paull, O; Wong., J; Sando, D; Lee, WT; Holt, SA; Valanoor, NInteractions at interfaces of magnetic materials such as giant magnetoresistance (GMR) form the physical foundation of many technological devices in today’s market. Although GMR technologies are now somewhat dated, interactions at the interface between layers of oxide materials continue to demonstrate attractive mechanisms for technology applications due to the wide variety of available oxide materials as well as their ability to be well lattice-matched to form heterostructures. Magnetic thin-film superlattices made of 15 repetitions of La2/3Sr1/3MnO3 (LSMO) and LaNiO3 (LNO) have been shown to exhibit a magnetic exchange interaction in LNO that is dependent upon its thickness n (where n is the number of unit cells of LNO) between LSMO layers [1]. At n = 1, the LSMO layers are ferromagnetically aligned with eachother. At n = 3 however, the LSMO layers are canted by 110◦ with respect to one another. This canting is reportedly driven by an emergent c-axis spin-helix in LNO that arises due to charge transfer at the interfaces between LNO and LSMO [2]. We have fabricated superlattices of similar quality to Ref. [1] using Reflected High Energy Electron Diffraction (RHEED) assisted Pulsed Laser Deposition (PLD), where RHEED is used to ensure unit-cell precision in layer thicknesses. These superlattices have been designed so they exhibit n = 3 and n = 1 interactions within the same superlattice in a modulated pattern. This modulation of the effective LNO exchange interaction in these samples creates a toy model of coupled magnetic layers to explore. The modulated design of these samples create “frustrated” environments where the effective exchange interaction is different on each side of an LSMO layer within the superlattice. We utilise polarised neutron reflectometry using PLAYPUS to reveal the complex magnetic profile of these modulated superlattices by measuring the non-spin-flip (R++, R−−), and spin-flip (R+−, R−+) cross sections. Presented are the current progress and prospects in the fitting process of these complex datasets. © The authors.
- ItemThe CG1 instrument development test station at the high flux isotope reactor(Elsevier, 2011-04-01) Crow, L; Robertson, L; Bilheux, H; Fleenor, M; Iverson, E; Tong, X; Stoica, D; Lee, WTThe CG1 instrument development station at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory began commissioning operation in 2009. When completed, the station will have four beams. CG1A is a 4.22 angstrom monochromatic beam intended for spin-echo resolved grazing incidence scattering (SERGIS) prototype development. Initial beam operation and characterization are in progress. CG1B will be a 2.35 angstrom monochromatic beam for a 2-axis utility diffractometer for sample alignment and monochromator development. CG1C will have a double-bounce monochromator system, which will produce a variable wavelength beam from about 1.8-6.4 angstrom, and will be used for imaging and optical development. The CG1D beam is a single chopper time-of-flight system, used for instrument prototype and component testing. The cold neutron spectrum, with an integrated flux of about 2.7 x 10(9) n/cm(2) s, has a guide cutoff at 0.8 angstrom and useful wavelengths greater than 20 angstrom. Initial results from CG1 include spectral characterization, imaging tests, detector trials, and polarizer tests. An overview of recent tests will be presented, and upcoming instrument prototype efforts will be described. (C) 2010 Elsevier B.V. All rights reserved.
- ItemDirect evidence for the spin cycloid in strained nanoscale bismuth ferrite thin films(Australian Institute of Physics, 2017-01-31) Bertinshaw, J; Maran, R; Callori, SJ; Ramesh, V; Cheung, J; Dainlkin, SA; Lee, WT; Hu, S; Seidel, J; Valanoor, N; Ulrich, CMultiferroic materials demonstrate excellent potential for next-generation multifunctional devices, as they exhibit coexisting ferroelectric and magnetic orders. Bismuth ferrite (BiFeO3) is a rare exemption where both order parameters exist far beyond room temperature, making it the ideal candidate for technological applications. In particular, magnonic devices that utilize electric control of spin waves mediated by complex spin textures are an emerging direction in spintronics research. To realize magnonic devices, a robust long-range spin cycloid with well known direction is desired, since it is a prerequisite for the magnetoelectric coupling. Despite extensive investigation, the stabilization of a large-scale uniform spin cycloid in nanoscale (100 nm) thin BiFeO3 films has not been accomplished. Here, we demonstrate cycloidal spin order in 100 nm BiFeO3 thin films through the careful choice of crystallographic orientation, and control of the electrostatic and strain boundary conditions during growth [1]. Neutron diffraction, in conjunction with X-ray diffraction, reveals an incommensurate spin cycloid with a unique [112] propagation direction. While this direction is different from bulk BiFeO3, the cycloid length and Néel temperature remain equivalent to bulk single crystals. The discovery of a large scale uniform cycloid in thin film BiFeO3 opens new avenues for fundamental research and technical applications that exploit the spin cycloid in spintronic or magnonic devices.
- ItemDynamical theory calculations of spin-echo resolved grazing-incidence scattering from a diffraction grating(Wiley-Blackwell, 2010-06-01) Ashkar, R; Stonaha, P; Washington, AL; Shah, VR; Fitzsimmons, MR; Maranville, B; Majkrzak, CF; Lee, WT; Schaich, WL; Pynn, RNeutrons scattered or reflected from a diffraction grating are subject to a periodic potential analogous to the potential experienced by electrons within a crystal. Hence, the wavefunction of the neutrons can be expanded in terms of Bloch waves and a dynamical theory can be applied to interpret the scattering phenomenon. In this paper, a dynamical theory is used to calculate the results of neutron spin-echo resolved grazing-incidence scattering (SERGIS) from a silicon diffraction grating with a rectangular profile. The calculations are compared with SERGIS measurements made on the same grating at two neutron sources: a pulsed source and a continuous wave source. In both cases, the spin-echo polarization, studied as a function of the spin-echo length, peaks at integer multiples of the grating period but there are some differences between the two sets of data. The dynamical theory explains the differences and gives a good account of both sets of results. © 2010, Wiley-Blackwell.
- ItemFerromagnetic ordering in Mn-doped ZnO nanoparticles(Springer, 2014-01-01) Luo, X; Lee, WT; Xing, GZ; Bao, N; Yonis, A; Chu, D; Lee, J; Ding, J; Li, S; Yi, JBZn1 - xMn x O nanoparticles have been synthesized by hydrothermal technique. The doping concentration of Mn can reach up to 9 at% without precipitation or secondary phase, confirmed by electron spin resonance (ESR) and synchrotron X-ray diffraction (XRD). Room-temperature ferromagnetism is observed in the as-prepared nanoparticles. However, the room-temperature ferromagnetism disappears after post-annealing in either argon or air atmosphere, indicating the importance of post-treatment for nanostructured magnetic semiconductors.© 2014 Luo et al.; licensee Springer.
- ItemFerromagnetism of Co, Eu Co-doped ZnO and 5%-Co doped TiO2 magnetic semiconductors(Australian Institute of Physics, 2014-02-04) Lee, OJ; Lou, X; Lee, WT; Lauter, V; Triani, G; Li, S; Yi, JBDiluted magnetic semiconductor has attracted wide interest due to its potential applications in spintronics devices. Oxide semiconductor based diluted magnetic semiconductors has been investigated in detail for possible ferromagnetism above room temperature. However, most of the diluted magnetic semiconductors show very weak ferromagnetism. The magnetic moment is originated from the doped magnetic element, such as Fe, Co, Ni. Rare-earth element, which shows strong spin-orbit coupling, may enhance the magnetic anisotropy of the diluted magnetic semiconductors, thus enhances the ferromagnetism. In this work, we used both Co and Eu to co-dope ZnO and deposited Co doped TiO2 thin films in order to achieve a diluted room-temperature magnetic semiconductor with strong ferromagnetism. 4%Co and 4%Eu or 6% Eu were used for the doping by implantation in ZnO and 5%Co-TiO2 film were deposited on LaAlO3 substrate under different oxygen partial pressures from 10-4 to 10-6 torr. For the ZnO-based thin films, XRD analysis indicates there is no secondary or impurity phase. Magnetic measurement by SQUID shows room temperature ferromagnetism. Polarized neutron reflectometry (PNR) analysis illustrates that ZnO film is 100 nm in thickness and the magnetic layers is around 30 nm, which is in consistent with the penetration depth of Co and Eu implantation, indicating the magnetic moment is due to the Co and Eu co doping. 4%Co, 4%Eu codoped ZnO film has a saturation magnetization of 3.57 emu/cm3, while 4%Co, 6%Eu co doped ZnO film has a saturation magnetization of 9.62 emu/cm3, indicating the significant enhancement of saturation magnetization by more rare earth element doping. For the TiO based thin films, XRD analysis show epitaxial growth and that the films have anatase phases. TEM confirms the single crystal like microstructure. EDX mapping indicates that Co is uniformly distributed in the TiO2 matrix, suggesting effective doping of Co dopant. Magnetic measurement shows that film deposited under lower oxygen partial pressure has a larger saturation magnetization. PNR shows that the magnetization is uniformly distributed along the film thickness. The magnetization for the film deposited under an oxygen partial pressure of 10-6 torr is about 4.2 emu/cm3, which is much smaller than that measured by SQUID (30 emu/cm3). This suggests a magnetic dead layer on the film surface.
- ItemIn-situ polarized 3 He-based neutron polarization analyzer for SNS magnetism reflectometer(Insitute of Physics, 2010-12-16) Lee, WT; Tong, X; Pierce, J; Fleenor, M; Ismaili, A; Robertson, JL; Chen, WC; Gentile, TR; Hailemariam, A; Goyette, R; Parizzi, A; Lauter, V; Klose, F; Kaiser, H; Lavelle, C; Baxter, DV; Jones, GL; Wexler, J; McCollum, LWe report here the construction and neutron transmission test results of an in-situ polarized 3 He-based neutron polarization analyzer system for the Magnetism Reflectometer at the Spallation Neutron Source, Oak Ridge National Laboratory. The analyzer uses the Spin-Exchange Optical Pumping method to polarize the 3 He nuclei of a cell of 3 He gas. Polarized neutrons scattered from the sample are intercepted by the polarized 3 He gas which strongly absorbs neutrons in one spin-state while allowing most neutrons in the other spin-state to pass through. To maintain a stable analyzing efficiency during an experiment, the 3 He gas is continuously polarized in - situ on the instrument. Neutron transmission measurements showed that 73% 3 He polarization was reached in this setup. © 2010, Insitute of Physics.
- ItemMagnetic ordering in superconducting sandwiches(Australian Institute of Physics, 2020-02-04) Chan, A; van der Heijden, NJ; Söhnel, T; Simpson, MC; Rule, KC; Causer, GL; Lee, WT; Bernard, C; Mallett, BPPOur cuprate-manganite ‘superconducting sandwich’ multilayers exhibit a highly unusual magnetic-field induced insulating-to-superconducting transition, contrary to the commonly held understanding that magnetic fields are detrimental to superconductivity. This new behaviour is a result of the specific magnetic and electronic properties of the manganite coupling with the cuprate (YBa2Cu3O7-δ, YBCO). Due to the specific manganite composition, Nd0.65(Ca0.7Sr0.3)0.35MnO3 (NCSMO), we hypothesize the behaviour to originate from CE-type antiferromagnetic ordering as well as charge and orbital ordering. Zero-field cooled polarized neutron reflectometry (PNR) data in Fig 1(A) shows a sizable spin-flip (R+-) signal which may result from disordered ferromagnetic domains which sum to give a vanishing macroscopic magnetization. Initial elastic neutron scattering measurements performed on 100 nm thin film NCSMO display signatures of magnetic ordering (Fig 1(B)). Future neutron scattering measurements will look at the modification of magnetic order in a superlattice to better understand the relationship between NCSMO magnetization and our newly discovered insulating-to-superconducting transition.
- ItemMagnetic structures of magnetocaloric (Mn1-xNix)CoGe and Mn(Co1-xNix)Ge alloys(Australian Institute of Nuclear Science and Engineering, 2016-11-29) Ren, QY; Hutchison, WD; Wang, JL; Studer, AJ; Lee, WT; Cadogan, JM; Campbell, SJThe magnetocaloric effect (MCE) - a significant temperature change around the magnetic transitions in materials driven by magnetisation or demagnetisation - has emerged as an increasingly important topic in condensed matter physics in the past two decades. This development is due primarily to potential applications in refrigeration as an alternative to gas-based compression-expansion refrigeration [1]. A large MCE occurs generally around a magnetic transition, especially when the magnetic transition coincides with a structural transition (magneto-structural transition) [1]. MnCoGe-based compounds offer particular scope for MCE applications, particularly for cooling around room temperature with previous studies having shown that it is relatively straightforward to engineer the structural transition temperature and thereby produce a magneto-structural transition [2]. In the present work, a series of (Mn1-xNix)CoGe (x = 0.0-0.07) and Mn(Co1-xNix)Ge (x = 0.14-1.00) samples have been prepared in order to investigate the effects of doping the Mn and Co sites of MnCoGe with Ni. The crystal structures and magnetisation were measured using XRD (20-310 K) and PPMS (5-320 K) with the magneto-structural transitions studied using neutron powder diffraction and polarised neutron diffraction (5-450 K; WOMBAT, OPAL). Magneto-structural transitions from ferromagnetic-orthorhombic (FM-Orth) structure to paramagnetic-hexagonal (PM-Hex) structure were obtained in both (Mn1-xNix)CoGe and Mn(Co1-xNix)Ge around room temperature. A spiral antiferromagnetic (SP-AFM) structure was also observed in the orthorhombic structure of Mn(Co1-xNix)Ge (x ≥ 0.55) at low temperature, following by a magnetic transition from SP-AFM to FM at higher temperature. In addition, the influence of magnetic field on the FM-Orth/PM-Hex magneto-structural transition was studied using field dependent neutron diffraction (5-320 K; 0-9 T). Our investigations show that normal (inverse) MCE are obtained around the FM-Orth/PM-Hex (SP-AFM/FM) transitions in (Mn1-xNix)CoGe and Mn(Co1-xNix)Ge.
- ItemNeutron spin evolution through broadband current sheet spin flippers(American Institute of Physics, 2013-10-01) Stonaha, P; Hendrie, J; Lee, WT; Pynn, RControlled manipulation of neutron spin is a critical tool for many neutron scattering techniques. We have constructed current-sheet, neutron spin flippers for use in Spin Echo Scattering Angle Measurement (SESAME) that comprise pairs of open-faced solenoids which introduce an abrupt field reversal at a shared boundary. The magnetic fields generated by the coils have been mapped and compared with both an analytical approximation and a numerical boundary integral calculation. The agreement is generally good, allowing the former method to be used for rapid calculations of the Larmor phase acquired by a neutron passing through the flipper. The evolution of the neutron spin through the current sheets inside the flipper is calculated for various geometries of the current-carrying conductors, including different wire shapes, arrangements, and common imperfections. The flipping efficiency is found to be sensitive to gaps between wires and between current sheets. SESAME requires flippers with high fields and flipping planes inclined to the neutron beam. To avoid substantial neutron depolarization, such flippers require an interdigitated arrangement of wires. © 2013, American Institute of Physics.
- ItemPerformance test on neutron polarization analysis capability of PELICAN –time of flight cold neutron spectrometer(International Conference on Neutron Scattering, 2017-07-12) D'Adam, TM; Lee, WT; Mole, RA; Yu, DHThe implementation of polarization analysis on a conventional time-of-flight spectrometer has been a major instrumental goal for some time. Here we present our recent results describing our successful test of the polarization analysis option on the PELICAN spectrometer. The compact incident neutron polarization system is an integration of a solid-state bender-type supermirror polarizer with a gradient radio frequency (RF) spin flipper. Polarization analysis is achieved by using a polarized 3He neutron spin filter that covers a span of 120 degrees. The polarization analysis system is installed inside the high vacuum sample chamber through a dedicated aluminium vacuum adaptor flange. In-situ refilling of pre-generated polarized 3He gas has been implemented. The supermirror polarizer and spin flipper have been characterized with a Heusler crystal as the analyser for neutron wavelength of 4.68 Å. 95% polarization efficiency and 92% flipping efficiency have been obtained for the polarizer and spin flipper, respectively. It was found that the Fermi chopper had no depolarization effects. Further tests with the 3He analyse ron a non-magnetic alumina sample achieved overall polarization efficiency of 82% and this gives 94% analysing power for a 3He analyser filled with 1 bar of 3He gas. The T1 lifetime of the 3He cell is about 100 hours. Nuclear-spin incoherent scattering on vanadium has been performed and the 2:1 ratio between the spin-flip and non-spin-flip signal has been observed. The energy resolution of the conventional spectrometer was maintained and approximately 80 % of the detector area is still useable. More details of the instrument performance and further improvement on polarization analysis will be presented.
- ItemPolarised 3He based neutron polarisers and analysers for magnetism research on ANSTO instruments(Australian Institute of Physics, 2012-02-02) Lee, WT; Klose, F; Jullien, D; Andersen, KHPolarised 3He based neutron polariser and polarization analyser [1] have become a matured technology for polarised neutron experimental works. A joint project of the Australian Nuclear Science and Technology Organisation (ANSTO) and the Institute Laue Langevin (ILL) is underway to provide 6 OPAL neutron scattering instruments with these important research capabilities. The instruments include SANS Quokka, diffractometer Wombat, thermal triple-axis spectrometer Taipan, reflectometer Platypus, Taipan’s cold-neutron counterpart Sika, and cold neutron time-of-flight spectrometer Pelican. Discussions are underway to further expand the use to more instruments, including the Laue diffractometer Koala and new instruments that are being designed and constructed. The project will produce a 3He gas polarizing station that uses the Metastable Exchange Optical Pumping method [2]. Silicon-window polarised 3He cells will polarize the incident neutron beam on several instruments and analyse the scattered neutrons on Platypus and Quokka. Wide-angle analyser “Pastis” cells [3] will be used for Wombat and Pelican. The polarizers and analysers are housed in magnetio-static cavities “Magic Box” and “Pastis” uniform field coils. The polarizing station has passed major performance requirements. The equipment for use on instruments are being built and tested for 3He polarisation lifetime, and infrastructural changes are being incorporated on ANSTO instruments. This presentation will provide examples illustrating the use of polarised neutrons to study magnetic materials and explain the methodology for using this technique. The latest status of the polarizing station and test results of the instrument components will be presented.
- ItemPolarised neutron diffraction study of the spin cycloid in strained nanoscale bismuth ferrite thin films(Australian Institute of Physics, 2017-01-31) Lee, WT; Bertinshaw, J; Maran, R; Callori, SJ; Ramesh, V; Cheung, J; Danilkin, SA; Hu, S; Seidel, J; Valanoor, N; Ulrich, CPolarised neutron scattering is capable of separating magnetic structure from chemical structure. Here we report an experiment using the newly available capability at ANSTO, namely polarised neutron diffraction using polarised 3He neutron spin-filters to obtain the detail magnetic structure in even highly complex magnetic materials. Magnonic devices that utilize electric control of spin waves mediated by complex spin textures are an emerging direction in spintronics research. Room-temperature multiferroic materials, such as BiFeO3, with a spin cycloidal structure would be ideal candidates for this purpose. In order to realise magnonic devices, a robust long-range spin cycloid with well-known direction is desired. Despite extensive investigation, the stabilization of a large scale uniform spin cycloid in nanoscale (100 nm) thin BiFeO3 films has not been accomplished. The polarized neutron diffraction experiment did confirm the existence of the spin cycloid in this BiFeO3 film, which is an important prerequisite for the multiferroic coupling.
- ItemPolarised neutrons for material science research at ANSTO(Australian Institute of Physics, 2018-01-31) Lee, WT; D'Adam, TMPolarised neutron scattering can definitively identify magnetic structures and dynamics, and separate the structural signal and the spin-incoherent scattering in hydrogen-rich materials. At ANSTO, our project to incorporate this capability to a wide suit of instruments is coming to fruition. User research experiments using polarised neutrons have recently been carried out to study multiferroic and magnetostrictive materials on the TAIPAN thermal triple-axis spectrometer and WOMBAT high-intensity diffractometer, and from an earlier time, magnetic multilayers on the PLATYPUS reflectometer. One of the first round of user research has been published. We have now also completed the deployment and test on the PELICAN cold neutron chopper spectrometer, QUOKKA SANS instrument and SIKA cold triple-axis spectrometer. Condensed matter research experiments will be carried out on those three instruments in the first half of 2018. The ECHIDNA high-resolution diffractometer is the next instrument to acquire this capability. Our development focus is now on providing user support to plan experiment, reduce data and analyse data: Rather than a surveying technique, a polarised neutron experiment is often done in the regions of interest identified using unpolarised neutron measurements. The type of polarizer and analyser (often polarised Helium-3 based) would affect what and how the measurements will be done. And polarised neutron data reduction and analysis would add a level of complexity to the process. This presentation will provide an overview of the capabilities available, some of the experiments that had been carried out to illustrate how material research can utilize polarised neutrons and the key factors to consider in planning an experiment and reducing the data.
- ItemPolarised neutrons for materials research on OPAL instruments(Australian Institute of Physics, 2015-02-03) Lee, WTPolarised neutron scattering is a powerful technique to study magnetism and to enhance the signal-to-noise in the studies of hydrogen-rich materials in biology and organic chemistry. Polarisation analysis unambiguously identifies the scattering pattern of the magnetic structure and excitation and determines the direction of magnetic moment and excitation. Using polarisation analysis in neutron scattering to measure hydrogen-rich materials, we can separately measure the structural signal and the amount of hydrogen in the material, which has long been a challenge in studying organic materials. At ANSTO, polarisation analysis has previously been available on the reflectometer PLATYPUS for thin film and multilayer studies. The operation of a 3He Polarising Station has now provide this capability to the WOMBAT diffractometer for determining magnetic structure down to the atomic level and to the TAIPAN triple-axis spectrometer for studying magnetic excitation and structure. During commissioning tests, we have discovered new details of magnetic structure in multiferroic samples on both instruments. This new development will soon be followed by polarised SANS capability on QUOKKA for magnetic nano-particle and hydrogen-rich material research. Off-specular magnetic scattering on reflectometer PLATYPUS and polarised inelastic scattering on spectrometers PELICAN and SIKA will be made available in the coming months.
- ItemPolarised neutrons for materials sciences research at the Australian Nuclear Science and Technology Organisation (ANSTO)(Australian Institute of Physics, 2014-02-04) Lee, WT; Studer, AJ; Rule, KC; Danilkin, SA; Yu, DH; Mole, RA; Kennedy, SJ; Gilbert, EP; Wood, K; Klose, F; D'Adam, TMPolarised neutron scattering has been used extensively to study magnetism in materials. Diffraction allows us to resolve the distribution and orientation of the magnetic moments down to the atomic scale. Inelastic scattering studies the magnetic excitations. The complex magnetic structure in magnetic nanoparticles is a hot topic for Small Angle Neutron Scattering (SANS). Novel magnetic thin film and multilayer are the subjects of neutron reflectometry. The technique is also increasingly being used to significantly enhance the signal-to-noise ratio in SANS measurement of hydrogen-rich materials. At ANSTO, polarised neutron option is currently available on both the SANS instrument “Quokka” (incident beam) and the reflectometer “Platypus” (incident and scattered beam). Recent technological advance of polarised Helium-3 based neutron spin-filter technique has opened up the possibility of using polarised neutrons on a wider range of instruments. In addition to enhancing the capabilities of Quokka (both incident and scattered beam for hydrogen-rich material and magnetic nanoparticle studies) and Platypus (wide-angle analysis for e.g. patterned magnetic surface structure), we are installing and testing polarised neutron equipment on the diffractometer “Wombat” and inelastic-scattering instruments “Taipan”, “Pelican” and “Sika”. This new capability will become available for experiments from July 2014. Furthermore, a new supermirror polariser is being commissioned on Pelican for polarised inelastic scattering work. In this presentation, examples illustrating the technique and use of polarised neutron scattering and the current status of installation and test on instruments will be provided.
- ItemSpin exchange optical pumping based polarized He-3 filling station for the hybrid spectrometer at the spallation neutron source(American Institute of Physics, 2013-06-01) Jiang, CY; Tong, X; Brown, DR; Culbertson, H; Graves-Brook, MK; Hagen, ME; Kadron, B; Lee, WT; Robertson, JL; Winn, BThe Hybrid Spectrometer (HYSPEC) is a new direct geometry spectrometer at the Spallation Neutron Source at the Oak Ridge National Laboratory. This instrument is equipped with polarization analysis capability with 60 degrees horizontal and 15 degrees vertical detector coverages. In order to provide wide angle polarization analysis for this instrument, we have designed and built a novel polarized He-3 filling station based on the spin exchange optical pumping method. It is designed to supply polarized He-3 gas to HYSPEC as a neutron polarization analyzer. In addition, the station can optimize the He-3 pressure with respect to the scattered neutron energies. The depolarized He-3 gas in the analyzer can be transferred back to the station to be repolarized. We have constructed the prototype filling station. Preliminary tests have been carried out demonstrating the feasibility of the filling station. Here, we report on the design, construction, and the preliminary results of the prototype filling station. © 2013, American Institute of Physics.
- ItemStability and scaling behavior of the spin cycloid in BiFeO3 thin films(Australian Institute of Physics, 2018-01-30) Burns, SR; Sando, D; Bertinshaw, J; Russell, L; Xu, X; Maran, R; Callori, SJ; Ramash, V; Cheung, J; Danilkin, SA; Deng, G; Lee, WT; Hu, S; Bellaiche, L; Seidel, J; Valanoor, N; Ulrich, CMultiferroic materials demonstrate excellent potential for next-generation multifunctional devices, as they exhibit coexisting ferroelectric and magnetic orders. Bismuth ferrite (BiFeO3) is a rare exemption where both order parameters exist far beyond room temperature, making it the ideal candidate for technological applications. To realize magnonic devices, a robust longrange spin cycloid with well-known direction is desired, since it is a prerequisite for the magnetoelectric coupling. Despite extensive investigation, the stabilization of a large-scale uniform spin cycloid in nanoscale (<300 nm) thin BiFeO3 films has not been accomplished. Using neutron diffraction we were able to demonstrate cycloidal spin order in 100 nm BiFeO3 thin films which became stable through the careful choice of crystallographic orientation and control of the electrostatic and strain boundary conditions during growth [1]. Furthermore, Co-doping, which has demonstrated to further stabilize the spin cycloid, did allow us to obtain spin cycloid order in films of just 50 nm thickness, i.e. films thinner than the cycloidal length of about 64 nm. Interestingly, in thin films the propagation direction of the spin cycloid has changed and shows a peculiar scaling behavior for thinnest films. We were able to support these observations by Monte Carlo theory based on a first-principles effective Hamiltonian method. Our results therefore offer new avenues for fundamental research and technical applications that exploit the spin cycloid in spintronic or magnonic devices.
- ItemStabilization of spin and charge ordering in stoichiometric YbFe2O4(Physical Society of Japan, 2019-03-15) Fujiwara, K; Karasudani, T; Kakurai, K; Lee, WT; Rule, KC; Studer, AJ; Ikeda, NWe report a wide-range reciprocal space observation with neutron diffraction in an iron vacancy controlled YbFe2O4 crystal, which is proposed as a prototype of electronic ferroelectrics arising from iron charge ordering. The increase of the charge ordering transition temperature and the disappearance of spin competitive transition were discovered in this stoichiometric crystal. We suppose that the lower ionic deficiency of this crystal enhances the development of spin and charge order coherence length, and consequently, the intrinsic nature of spin and charge ordering of YbFe2O4 could be detected. The experiment was performed with a two-dimensional neutron detector, and all super-lattice spots and its modulations above magnetic ordering temperature TN = 245 K are successfully explained with six domains of a monoclinic charge-order super-lattice cell. A rather extended two dimensional (2D) spin correlation above TN was identified with polarized 3He neutron spin filter and we found a clear indication of a coupling between the 2D spin correlation and charge ordering between TN and 300 K, at which a new lattice distortion phase may set in. ©2019 The Physical Society of Japan.
- ItemTemperature dependence of structural parameters of the layered magnetic glass Fe0.5Ni0.5PS3(Australian Institute of Physics, 2014-02-05) Goossens, DJ; Lee, WT; Studer, AJThe layered magnetic materials of the MPS3 family (M=2+ metal) show a wide range of behaviours. Recently, magnetic glassiness, with a relaxation time of the order of an hour, was observed in Fe0.5Ni0.5PS3. The relaxation depends on sample history, both thermal and applied magnetic field. Here some aspects of the behaviour of the magnetic and crystal structure with temperature and field are explored using the Wombat powder diffractometer at ANSTO. Diffuse scattering can be seen to decrease as temperature falls and to fall sharply at the magnetic transition, and at different scattering vector Q to the magnetic Bragg peaks. This suggests a short-range ordered magnetic structure with different spin-spin correlations to the long-range ordered structure.