Browsing by Author "Nishimura, K"

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    Determination 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, K
    Recent 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.
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    Determination 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, K
    The 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.
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    Determination 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, K
    There 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.
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    Evolution with applied field of the magnetic structure of TbNiAl4
    (Springer Link, 2014-12-17) White, R; Hutchison, WD; Goossens, DJ; Studer, AJ; Nishimura, K
    Neutron 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.
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    Field-induced incommensurate spin structure of TbNiAl4
    (American Physical Society, 2012-07-13) Hutchison, WD; Goossens, DJ; Whitfield, RE; Studer, AJ; Nishimura, K; Mizushima, T
    TbNiAl(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.
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    Incommensurate magnetic order in PrNiAl4
    (Australian and New Zealand Institutes of Physics, 2016-02-02) White, RD; Hutchison, WD; Avdeev, M; Nishimura, K
    The 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.
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    Magnetic order studies of ErNiAl4
    (Australian Institute of Physics, 2007-02-06) Hutchison, WD; Goossens, DJ; Saensunon, B; Stewart, GA; Avdeev, M; Nishimura, K
    Specific heat measurements on ErNiAl4 show a phase transition at 5.8(1) K. Magnetisation data confirms the low temperature phase is antiferromagnetic in nature, while neutron powder diffraction data suggests an incommensurate structure similar to the intermediate magnetic phase of TbNiAl4.