Browsing by Author "Hutchison, WD"
Now showing 1 - 20 of 51
Results Per Page
Sort Options
- Item18O isotope substitution on the multiferroic compound DyMnO3(Australian Institute of Physics, 2013-02-06) Narayanan, N; Li, F; Hutchison, WD; Reynolds, NM; Rovillain, P; Ulrich, C; Hester, JR; McIntyre, GJ; Mulders, AMNot available
- ItemCrystal and magnetic structure of (1-x)BiFeO3-xSrTiO3 (x=0.2, 0.3, 0.4 and 0.8)(Elsevier, 2013-11-01) Goossens, DJ; Weekes, CJ; Avdeev, M; Hutchison, WDThe effect of doping SrTiO3 into BiFeO3 on the magnetic and crystal structure has been explored using powder neutron diffraction for (1−x)BiFeO3–xSrTiO3(1−x)BiFeO3–xSrTiO3 where x=0.2, 0.3, 0.4, 0.6 and 0.8. While the data are not sensitive to the cycloidal component of the magnetic ordering, the evolution of the collinear antiferromagnetic moment of the G-type antiferromagnetic component with T and x has been explored, as have structural parameters. It is found that for x≤0.4x≤0.4 pure phase samples form in the R3c cell, and for x =0.8 a non-magnetic Pm3¯m phase is obtained. The x=0.6 sample gives a mixed phase. Through the R3c phase the magnetic structure does not change appreciably apart from the reduction of magnetic moment magnitude with the increasing T and/or x. © 2013, Elsevier Inc.
- ItemDetermination of the crystal field levels in TmV2Al20(Australian Institute of Physics, 2018-01-31) Hutchison, WD; White, R; Stewart, GA; Iles, GN; Mole, RA; Cadogan, JM; Namiki, T; Nishimura, KThe interest in compounds of the RM2Al20-type (R = lanthanide, M = transition metal) in recent years reflects the fascinating physical and magnetic properties on display at low temperatures. For example, in PrV2Al20 and PrTi2Al20 the phenomena reported include a quadrupolar Kondo effect [1] and superconductivity [2]. Central to such systems is the cubic symmetry of the Pr3+ site inducing a non-magnetic ground state in the ion. As a hole analogue of the PrV2Al20 compound, TmV2Al20 has been investigated in the hope of observing similar phenomena at low temperatures. At last year’s ‘Wagga’ we reported that we had determined the Tm3+ crystal field parameters W = 0.42(1) and x = -0.63(1) [3] (based on the Lea, Leask and Wolf formalism [4]) for TmV2Al20 using inelastic neutron scattering on PELICAN at the OPAL reactor, Lucas Heights. However, the line shapes found were extremely broad Lorentzians, indicative of a coupling of crystal field states to conduction electrons, ‘smearing out’ the energy required for transitions. Here, we report more recent developments: Tm3+ electron spin resonance results together with modelling of physical properties lead to the conclusion that there is a small local distortion away from cubic symmetry.
- ItemDetermination of the crystal field levels in TmV2Al20(Australian Institute of Physics, 2017-01-31) White, R; Hutchison, WD; Iles, GN; Mole, RA; Cadogan, JM; Namiki, T; Nishimura, KRecent interest in so called caged rare earth compounds of the RM2Al20-type (R = lanthanide, M = transition metal) follow from their fascinating physical and magnetic properties at low temperatures. Recent work on PrV2Al20 and PrTi2Al20 revealed unusual phenomena, including a quadrupolar Kondo effect and superconductivity, brought about by the cubic symmetry of the Pr3+ site inducing a non-magnetic ground state in the ion. As a hole analogue of the PrV2Al20 compound, TmV2Al20 has been investigated for equivalent heavy Fermion behaviour at low temperatures. In previous work, specific heat and magnetisation data were modelled with the crystal field parameters W = 0.5 K and x = -0.6 based on the Lea, Leask and Wolf formalism. However, the experimental zero field specific heat near 0.5 K could only be matched in the modelled curves using an artificial ground state broadening. In this work inelastic neutron scattering data obtained from the PELICAN time of flight spectrometer located at the OPAL reactor, Lucas Heights has allowed further refinement of the values to W = 0.42(1) K and x = -0.63(1). In addition the CEF transitions are found to be very broad, as required for the specific heat, and suggestive of strong 4f-conduction electron coupling.
- ItemDetermination of the crystal field levels in TmV2Al20(International Conference on Neutron Scattering, 2017-07-12) White, R; Hutchison, WD; Iles, GN; Mole, RA; Cadogan, JM; Namiki, T; Nishimura, K.So called caged rare earth compounds of the RM Al20-type (R = lanthanide, M = transition metal) exhibit interesting physical and magnetic properties at low temperatures. For example PrV Al20 and PrTi Al20 show a quadrupolar Kondo effect [1] and superconductivity [2] brought about by the non-magnetic ground state and the cubic symmetry of the Pr3+site. In this work the compound TmV Al20, a hole analogue of PrV Al20 has been investigated. Previous crystal field calculations based on specific heat and magnetisation [3] resulted in parameters of W = 0.5 K and x = -0.6 within the Lea, Leask and Wolf formalism [4]. However to match the experimental zero field specific heat near 0.5 K, an artificial broadening of the ground state was applied. To validate and clarify these results, we have carried out an inelastic neutron scattering experiment on the PELICAN time-of-flight spectrometer to determine the energy splitting between the crystal field levels. This has allowed a further refinement of the crystal field parameters to W = 0.42(1) K and x = -0.63(1). The very broad Lorentzian line shapes suggest strong 4f-conduction band electron coupling.
- ItemDetermination of the crystal field levels in TmV2Al20(Australian Institute of Nuclear Science and Engineering, 2016-11-29) White, R; Hutchison, WD; Iles, GN; Mole, RA; Cadogan, JM; Nishimura, KThere has been increasing interest in compounds of the RM2Al20-type (R = lanthanide, M = transition metal) in recent years due to the unique physical and magnetic properties many have been shown to display at low temperatures. Recent work carried out on PrV2Al20 and PrTi2Al20 has revealed a number of interesting phenomena, including a quadrupolar Kondo effect [1, 2] and superconductivity [3, 4] brought about by the cubic symmetry of the Pr3+ site inducing a non-magnetic ground state in the ion. As a hole analogue of the PrV2Al20 compound, TmV2Al20 has been investigated to see whether it too displays such phenomena at low temperatures. Crystal field calculations based on specific heat and magnetisation have been carried out previously [5] with parameters W = 0.5 K and x = -0.6 determined based on the Lea, Leask and Wolf formalism [6]. These results have been further refined to W = 0.42(1) K and x = -0.63(1) using inelastic neutron scattering data obtained from the PELICAN time-of-flight spectrometer located at the OPAL reactor, Lucas Heights.
- ItemThe effect of oxygen isotopes substitution on magnetism in multiferroic CaMn7O12(Australian Institute of Nuclear Science and Engineering, 2012-11-15) Li, F; Narayanan, N; Hutchison, WD; Ulrich, C; McIntyre, GJMultiferroic materials, where ferroelectricity and ferromagnetism coexist and interact and one property can be used to drive the other, can find potential applications in spintronics and information technology and form the basis for four-state memory. However the details of coupling between these two orders are not yet understood. Competing theories of inherent electronic structure and ionic displacement are proposed to explain this coupling, but no experimental evidence currently exists to differentiate these models. To investigate the interaction between magnetic moments and electric dipoles on a fundamental level, this study will extend the isotopic pure oxygen substitution, a widely used technique for the investigation of high temperature superconductors, to multiferroics. Single crystal CaMn{sub 7}0{sub 12} showing the largest magnetically induced electric polarization measured to date is chosen as a test material and synthesized by flux method. The preliminary results show that single crystals of a size —100x100x100 μm can be obtained however a small amount of CaMn 3 0 6 impurity phase is also detected in XRD. Efforts on growing a larger single crystal are under way.
- ItemEffects of 18O isotope substitution in multiferroic RMnO3 (R = Tb, Dy)(Australian Institute of Physics, 2016-02-05) Graham, PJ; Narayanan, N; McIntyre, GJ; Hutchison, WD; Ulrich, C; Reynolds, N; Rovillain, P; Hester, JR; Kimpton, JA; Yethiraj, M; Pomjakushina, E; Condor, K; Kenzelmann, MMultiferroic materials demonstrate desirable attributes for next-generation multifunctional devices as they exhibit coexisting ferroelectric and magnetic orders. In type-II multiferroics, coupling exists that allows ferroelectricity to be manipulated via magnetic order and vice versa, offering potential in high-density information storage and sensor applications. Despite extensive investigations into the subject, questions of the physics of magnetoelectric coupling in multiferroics remain, and competing theories propose different mechanisms. The aim of this investigation was to study changes in the statics and dynamics of structural, ferroelectric and magnetic orders with oxygen-18 isotope substitution to shine light into the coupling mechanism in multiferroic RMnO3 (R=Tb, Dy) systems. We have performed Raman spectroscopy on 16O and 18O-substituted TbMnO3 single crystals. Oxygen-18 isotope substitution reduces all phonon frequencies significantly. However, specific heat measurements determine no changes in Mn3+ (28 and 41 K) magnetic phase transition temperatures. Pronounced anomalies in peak position and linewidth at the magnetic and ferroelectric phase transitions. While the anomalies at the sinusoidal magnetic phase transition (41 K) are in accordance to the theory of spin-phonon coupling, further deviations develop upon entering the ferroelectric phase (28 K). Furthermore, neutron diffraction measurements on 16O and 18O-substituted DyMnO3 powders show structural deviations at the ferroelectric phase transition (17 K) in the order of 100 fm in the b direction. The Pbnm space group is centrosymmetric and therefore does not allow ferroelectricity via atomic displacements, however our Reitveld analysis for the subgroup P21 shows significant displacements and polarisation along b that is comparable to the experimental value, making it the most promising candidate for ionic displacement induced polarisation in DyMnO3. These combined results demonstrate that structure is an important consideration in the emergence of ferroelectricity in these materials.
- ItemEffects of 18O isotope substitution in multiferroic RMnO3 (R=Tb, Dy)(Australian Institute of Physics, 2015-02-02) Graham, PJ; Narayanan, N; Reynolds, NM; Li, F; Rovillain, P; Bartkowiak, M; Hester, JR; Kimpton, JA; Yethiraj, M; Pomjakushina, E; Conder, K; Kenzelmann, M; McIntyre, GJ; Hutchison, WD; Ulrich, CMultiferroic materials demonstrate desirable attributes for next-generation multifunctional devices as they exhibit coexisting ferroelectric and magnetic orders. In type-II multiferroics, coupling exists that allows ferroelectricity to be manipulated via magnetic order and vice versa, offering potential in high-density information storage and sensor applications. Despite extensive investigations into the subject, questions of the physics of magnetoelectric coupling in multiferroics remain, and competing theories propose different mechanisms. The aim of this investigation was to study changes in the statics and dynamics of structural, ferroelectric and magnetic orders with oxygen-18 isotope substitution to shine light into the coupling mechanism in multiferroic RMnO3 (R=Tb, Dy) systems. We have performed Raman spectroscopy on 16O and 18O-substituted TbMnO3 single crystals. Oxygen-18 isotope substitution reduces all phonon frequencies significantly. However, specific heat measurements determine no changes in Mn3+ (28 and 41 K) magnetic phase transition temperatures. Pronounced anomalies in peak position and linewidth at the magnetic and ferroelectric phase transitions are seen. While the anomalies at the sinusoidal magnetic phase transition (41 K) are in accordance to the theory of spin-phonon coupling, further deviations develop upon entering the ferroelectric phase (28 K). Furthermore, neutron diffraction measurements on 16O and 18O-substituted DyMnO3 powders show structural deviations at the ferroelectric phase transition (17 K) in the order of 100 fm. These results indicate that the structure is actively involved in the emergence of ferroelectricity in these materials.
- ItemElement-specific depth profile of magnetism and stoichiometry at the La0.67Sr0.33MnO3/BiFeO3 interface(American Physical Society, 2014-07-11) Bertinshaw, J; Brück, S; Lott, D; Fritzsche, H; Khaydukov, Y; Soltwedel, O; Keller, T; Goering, E; Audehm, P; Cortie, DL; Hutchison, WD; Ramasse, QM; Arredondo, M; Maran, R; Nagarajan, V; Klose, F; Ulrich, CDepth-sensitive magnetic, structural, and chemical characterization is important in the understanding and optimization of physical phenomena emerging at the interfaces of transition metal oxide heterostructures. In a simultaneous approach we have used polarized neutron and resonant x-ray reflectometry to determine the magnetic profile across atomically sharp interfaces of ferromagnetic La0.67Sr0.33MnO3/multiferroic BiFeO3 bilayers with subnanometer resolution. In particular, the x-ray resonant magnetic reflectivity measurements at the Fe and Mn resonance edges allowed us to determine the element-specific depth profile of the ferromagnetic moments in both the La0.67Sr0.33MnO3 and BiFeO3 layers. Our measurements indicate a magnetically diluted interface layer within the La0.67Sr0.33MnO3 layer, in contrast to previous observations on inversely deposited layers [P. Yu et al., Phys. Rev. Lett. 105, 027201 (2010)]. Additional resonant x-ray reflection measurements indicate a region of altered Mn and O content at the interface, with a thickness matching that of the magnetic diluted layer, as the origin of the reduction of the magnetic moment.© 2014, American Physical Society.
- ItemESR studies of magnetocaloric PrMn2-xFexGe2(Australian Institute of Physics, 2014-02-05) Ren, QY; Hutchison, WD; Campbell, SJ; Wang, JLIn a recent paper, we investigated the magnetic structures, phase transitions and magnetocaloric entropy of PrMn1.6Fe0.4Ge2 by a combination of bulk magnetometry, 57Fe Mössbauer spectroscopy and electron spin resonance (ESR) over the temperature range 5-300 K. This work followed on from a broader study of the PrMn2-xFexGe2 family of compounds, in which it was found that with decreasing temperature from the paramagnetic region, three magnetic phase transitions have been detected for PrMn1.6Fe0.4Ge2. The transition temperatures and related magnetic structures (using the notation of [3]) the magnetic structures are: (i) paramagnetism to intralayer antiferromagnetism (AFl) at TN intra=370 K; (ii) AFl to canted ferromagnetism (Fmc) at TC inter∼230 K, and (iii) a third transition around TC Pr∼30 K with ferromagnetic ordering of the Pr sublattice resulting in the combined magnetic region (Fmc+F(Pr)). Here the ESR, focusing on the Pr3+ 4f magnetic moment and undertaken in the vicinity of the lowest transition temperature, is the subject of further analysis in order to correlate the observed resonant line/s and changes in g-factors with the phases mentioned above. In particular an aim is to link the increase in g factor of the Pr3+ ion (from g = 0.85 in the region above TC Pr∼30 K to g ~ 2.5 at 8 K) with the bulk moments measured via DC magnetisation.
- ItemEvolution with applied field of the magnetic structure of TbNiAl4(Springer Link, 2014-12-17) White, R; Hutchison, WD; Goossens, DJ; Studer, AJ; Nishimura, KNeutron powder diffraction data of TbNiAl4 has been re-examined using a representational analysis, allowing a new model of the magnetic structure to be deduced. The basis vectors obtained describe an ‘elliptical helix’ type structure in which the moments rotate in the ab-plane as one moves along the c-axis. This new model has been used to simulate the expected result of a Low Temperature Nuclear Orientation (LTNO) experiment involving 299 keV gamma-ray emission from the 160Dy daughter of aligned 160Tb nuclei. Results of the simulation along the a-axis appear to partly match currently existing experimental data, with good agreement in the magnitude of lost anisotropy. © 2014, Springer International Publishing.
- ItemField-induced incommensurate spin structure of TbNiAl4(American Physical Society, 2012-07-13) Hutchison, WD; Goossens, DJ; Whitfield, RE; Studer, AJ; Nishimura, K; Mizushima, TTbNiAl(4) exhibits incommensurate and commensurate magnetic ordering as a function of temperature. As a function of applied field it undergoes a series of magnetic phase transitions. The first of these transitions, into an intermediate spin arrangement, is the source of a large inverse magnetocaloric effect, an unusual result given that an aligning field is being applied. This has potential uses in magnetic cooling. Here, single-crystal neutron diffraction with applied magnetic field is used to obtain the intermediate field spin arrangement in TbNiAl(4). We find that not only does the applied field drive the system from commensurate to incommensurate ordering, but that the phase transition shows hysteresis such that a mixed state simultaneously showing commensurate and incommensurate antiferromagnetic ordering, along with ferromagnetism, can be obtained. © 2012, American Physical Society.
- ItemIncommensurate magnetic order in PrNiAl4(Australian and New Zealand Institutes of Physics, 2016-02-02) White, RD; Hutchison, WD; Avdeev, M; Nishimura, KThe RNiAl4 intermetallic series (where R = Ln3+) has been the subject of much investigation over a number of years. These compounds are known to possess some interesting magnetic behaviours including multiple magnetic phases and metamagnetism. TbNiAl4, ErNiAl4 and NdNiAl4 are all known to have incommensurate magnetic structures determined from neutron diffraction, whereas the presence of an incommensurate magnetic phase in PrNiAl4 is more tentative, based only on specific heat and magnetisation measurements. Recent neutron powder diffraction experiments have confirmed the presence of this incommensurate magnetic phase at 7 K and 7.5 K, well within the range of 6.9-8.1 K predicted by the specific heat data. Analysis of the diffraction patterns puts the propagation vector of the magnetic phase at k = (0.071(1), 1, 0), with the magnetic moments pointing along the a-axis.
- ItemLow-energy crystal field excitations observed using inelastic neutron scattering(Australian Institute of Physics, 2016-02-02) Iles, GN; Stewart, GA; Mole, RA; Hutchison, WD; Cadogan, SThe time-of-flight spectrometer, PELICAN, at ANSTO operates two choppers which provide a fixed initial energy of neutrons to the sample. Configuring the instrument to a wavelength of 4.75Å, sets this initial neutron energy to 3.6meV. By phasing the choppers, however, harmonic wavelengths can be obtained such as λ/2, etc. By measuring a powder sample of ErNiAl4 at λ/2 (λ = 4.75Å) we could observe a greater range of positive energy transfers (to the sample) and, after appropriate background removal, confirm the presence of an excitation at 7meV. This excitation represents the emission from the crystal field level at 7meV to 0meV confirming the result obtained in a previous experiment.
- ItemMagnetic and structural properties of intermetallic NdMn2-xTixSi2 compounds(Australian Optical Society, 2012-01-01) Din, MFM; Wang, JL; Zeng, R; Shamba, P; Hutchison, WD; Avdeev, M; Kennedy, SJ; Campbell, SJGiant magnetocalorie effects have been observed in NdMn2-xTixSi2 around the Curie Temperature Tc (with AB = 5-0 T.) The magnetic entropy charge decreases with increasing x from 27 J kg- K- for x=0 to 10 J kg- K- for x =0.3. Neutron investigations indicate that magnetostructural coupling contribution plays a critical role in the large value of magnetic entropy change.
- ItemMagnetic and structural transitions in magnetocaloric Mn(Co1-xNix)Ge alloys(Australian Institute of Physics, 2017-02-01) Ren, QY; Hutchison, WD; Wang, JL; Studer, AJ; Cadogan, JM; Campbell, SJThe magnetocaloric effect (MCE) - a significant temperature change due to the entropy change around 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. A direct (positive) MCE occurs around a magnetic transition from ferromagnetism (FM) to paramagnetism (PM), while an inverse (negative) MCE is obtained around a magnetic transition from antiferromagnetism (AFM) to FM. If such magnetic transitions couple with a structural transition, a first-order magneto-structural transition can form and hence strengthen the MCE. In this work, the magnetic and structural transitions have been tuned by substitution of Ni for Co in MnCoGe. The Mn(Co1-xNix)Ge samples (x = 0.14 - 1.00) were studied by magnetisation, x-ray and neutron powder diffraction measurements over the temperature range 5 - 450 K. Mn(Co1-xNix)Ge alloys have an orthorhombic (Orth) TiNiSi-type structure (Pnma) at low temperature with transformation to a hexagonal (Hex) Ni2In-type structure (P63/mmc) at the martensitic transformation temperature TM. The increase of the Ni content changes the orthorhombic phase from FM (x < 0.55) to spiral-AFM (x ≥ 0.55). In addition, the transformation temperature TM for the reverse martensitic transformation - from orthorhombic to hexagonal - decreases with Ni content x when x < 0.55 and then increases when x ≥ 0.55. The adjustment of TM leads to the occurrences of first-order FM-Orth/PM-Hex magneto-structural transitions and large values of the direct MCE in the samples with ~0.20 < x < ~0.60. Moreover, the spiral-AFM/FM magnetic transitions in the orthorhombic phase for samples with ~0.55 < x < ~0.75 result in an inverse MCE.
- ItemMagnetic and structural transitions tuned through valence electron concentration in magnetocaloric Mn(Co1–xNix)Ge(American Chemical Society, 2018-02) Ren, QY; Hutchison, WD; Wang, JL; Studer, AJ; Campbell, SJThe structural and magnetic properties of magnetocaloric Mn(Co1-xNix)Ge compounds have been studied. Two responses to the increase of valence electron concentration on substitution of Ni (3d84s2) for Co (3d74s2) in the orthorhombic phase (Pnma) are proposed: expansion of unit-cell volume and redistribution of valence electrons. We present experimental evidence for electronic redistribution associated with the competition between magnetism and bonding. This competition in turn leads to complex dependences of the reverse martensitic transformation temperature TM (orthorhombic to hexagonal (P63/mmc)) and the magnetic structures on the Ni concentration. Magnetic transitions from ferromagnetic structures below x = 0.50 to noncollinear spiral antiferromagnetic structures above x = 0.55 at low temperature (e.g., 5 K) are induced by modification of the density of states at the Fermi surface due to the redistribution of valence electrons. TM is found to decrease initially with increasing Ni content and then increase. Both direct and inverse magnetocaloric effects are observed. © 2018 American Chemical Society.
- ItemMagnetic interplay of Mn and Yb sites in YbMn2Si2 – crystal field splitting(Elsevier, 2020-12-10) Mole, RA; Cortie, DL; Hofmann, M; Wang, JL; Hutchison, WD; Yu, DH; Wang, XL; Campbell, SJThe crystal field splitting of YbMn2Si2 has been investigated over the temperature range 5–65 K using inelastic neutron scattering at a wavelength of 2.345 Å (resolution 800 μeV; dynamic range ∼10 meV). The excitation spectra have been analysed using a crystal field model above and below TN2, the temperature at which the collinear antiferromagnetic structure AFil transforms to the low-temperature structure in which the magnetic cell is doubled along the c-axis (TN1 = 526(4) K > T > TN2 = 32(2) K). The calculated excitation spectra show good agreement with the observed spectra for the unique environment of Yb3+ ions in the collinear antiferromagnetic structure AFil above TN2 and for the inequivalent sites of Yb3+ ions below TN2. This agreement has been obtained with a model for the low-temperature region in which a molecular field with optimal components in the x, y and z directions of Bx = 13.5 T, By = 65 T, Bz = 21.3 T is included. The pronounced components in the x and y directions are discussed in relation to the significant contraction of ∼0.1% of the c lattice parameter below the TN2 magnetic transition. © 2020 Published by Elsevier B.V.
- ItemMagnetic order and structural properties of Tb2Fe2Si2C(Elsevier, 2016-01-05) Susilo, RA; Cadogan, JM; Hutchison, WD; Avdeev, M; Cobas, R; Muñoz-Pérez, S; Campbell, SJThe structural and magnetic properties of Tb2Fe2Si2C have been investigated by bulk measurements (magnetisation and specific heat), X-ray diffraction, neutron powder diffraction and 57Fe Mössbauer spectroscopy over the temperature range 3 K–300 K Tb2Fe2Si2C is antiferromagnetic with a Néel temperature TN of 44(2) K. The magnetic structure can be described with a propagation vector k = [0 0 ] with the Tb magnetic moments ordering along the b-axis. We also observed strong magnetoelastic effects in particular along the a- and c-axes associated with the antiferromagnetic transition. The 57Fe Mössbauer spectra show no evidence of magnetic splitting down to 10 K, indicating that the Fe atom is non-magnetic in Tb2Fe2Si2C. © 2015 Elsevier B.V.
- «
- 1 (current)
- 2
- 3
- »