Browsing by Author "Hicks, TJ"

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    Diffuse neutron scattering studies of single crystal specimens of Fe3-x MnxSi
    (Australian and New Zealand Institutes of Physics, 1994-02-09) Ersez, T; Kennedy, SJ; Hicks, TJ; Kepa, H
    Polarized neutron diffuse scattering measurements have been made of two single crystal specimens of the ordered intermetallic compounds Fe2.45Mno.55Si (at room temperature and Fe2MnSi (above and below the re-ordering temperature). The difference between spin-flip and non-spin-flip scattering cross-sections for the (111) position gave a negative diffuse peak around a positive Bragg peak, being more pronounced for the Fe2.45Mno.55Si crystal. This is consistent with a loss of moment on the B(Fe/Mn) site with addition of Mn. Preliminary model fitting has suggested that Mn atoms cluster on their preferred B-site.
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    The elusive magnetic structure of FePS3
    (Australian Institute of Physics, 2003-02-04) Rule, KC; McIntyre, GJ; Kennedy, SJ; Hicks, TJ
    Laue diffraction patterns from a single crystal of FePS3 were recorded at temperatures above and below the Néel temperature TN = 120 K on the new thermal Laue diffractometer VIVALDI at the Institut Laue Langevin. Magnetic peaks were weaker and more extended than the nuclear peaks. The directions in reciprocal space of the magnetic reflections were found by reference to the nuclear peaks, and the magnetic reflections could then be readily located on the monochromatic diffractometer D19. The strongest magnetic peaks were found at 0.5, -0.5, 0.34 and 1.5, -0.5, 0.34 and symmetry related positions.
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    High luminosity time of flight with polarisation analysis: CeCu6
    (Elsevier, 2007-07-15) Harker, SJ; Hicks, TJ; Kennedy, SJ; Yu, DH
    The magnetic excitation spectrum of the heavy fermion system CeCu6 has been obtained by pseudo-randomly chopping the polarisation of the beam on LONGPOL and measuring the time of flight with polarisation analysis before the detectors. Separation of the magnetic part of the spectrum was made by changing the polarisation direction at the specimen. This method achieves a greater luminosity at the specimen compared with conventional methods at the expense of a background proportional to the total scattering from the specimen. The form of the spectrum is as expected with two transitions and considerable inelastic intensity centred oil zero energy transfer. The crystal field spectrum of the Ce3+ ion is considerably broadened by the Kondo nature of the system. An analysis of the experimental accuracy was made based on the statistical variation between the runs which make up the experiment. LONGPOL is a very slow instrument, based as it is on a thermal source with an incident wavelength of 3.6 A. The demonstrated possibility to obtain a spectrum incorporating polarisation analysis provides a basis to evaluate the usefulness of future implementation. © 2007, Elsevier Ltd.
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    Magnetic structure and magnon dynamics of the quasi-two-dimensional antiferromagnet FePS 3
    (American Physical Society, 2016-12-07) Lançon, D; Walker, HC; Ressouche, E; Ouladdiaf, B; Rule, KC; McIntyre, GJ; Hicks, TJ; Rønnow, HM; Wildes, AR
    Neutron scattering from single crystals has been used to determine the magnetic structure and magnon dynamics of FePS3, an S=2 Ising-like quasi-two-dimensional antiferromagnet with a honeycomb lattice. The magnetic structure has been confirmed to have a magnetic propagation vector of kM=[0112] and the moments are collinear with the normal to the ab planes. The magnon data could be modeled using a Heisenberg Hamiltonian with a single-ion anisotropy. Magnetic interactions up to the third in-plane nearest neighbor needed to be included for a suitable fit. The best fit parameters for the in-plane exchange interactions were J1=1.46, J2=−0.04, and J3=−0.96 meV. The single-ion anisotropy is large, Δ=2.66 meV, explaining the Ising-like behavior of the magnetism in the compound. The interlayer exchange is very small, J′=−0.0073 meV, proving that FePS3 is a very good approximation to a two-dimensional magnet. ©2016 American Physical Society
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    Magnetic structure of the quasi-two-dimensional antiferromagnet NiPS 3
    (American Physical Society, 2015-12-07) Wildes, AR; Simonet, V; Ressouche, E; McIntyre, GJ; Avdeev, M; Suard, E; Kimber, SAJ; Lançon, D; Pepe, G; Moubaraki, B; Hicks, TJ
    The magnetic structure of the quasi-two-dimensional antiferromagnet NiPS3 has been determined by magnetometry and a variety of neutron diffraction techniques. The experiments show that the samples must be carefully handled, as gluing influences the magnetometry measurements while preferred orientation complicates the interpretation of powder diffraction measurements. Our global set of consistent measurements show numerous departures from previously published results. We show that the compound adopts a k = [010] antiferromagnetic structure with the moment directions mostly along the a axis, and that the paramagnetic susceptibility is isotropic. The critical behavior was also investigated through the temperature dependence of the magnetic Bragg peaks below the Néel temperature. ©2015 American Physical Society
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    The magnon dynamics and spin exchange parameters of FePS3
    (IOP Publishing Ltd, 2012-10-17) Wildes, AR; Rule, KC; Bewley, RI; Enderle, M; Hicks, TJ
    The spin waves in a powdered sample of a quasi-two-dimensional antiferromagnet, FePS(3), have been measured using neutron inelastic scattering. The data could be modelled and the exchange interactions determined using a two-dimensional Heisenberg Hamiltonian with single ion anisotropy. A suitable fit to the data could only be achieved by including magnetic interactions up to the third nearest neighbour, which is consistent with the findings for other members of the MPS(3) family (M = transition metal). The best fit parameters at 6 K were J(1) = 1.49 meV, J(2) = 0.04 meV, J(3) = -0.6 meV, with an anisotropy of Delta = 3.7 meV. Measurements as a function of temperature give a coarse measure of the behaviour of the anisotropy and the nature of the phase transition. © 2012, IOP Publishing LTD.
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    A polarised neutron study of crystal field transitions in CeCu6
    (Australian Institute of Physics, 2004-02-04) Harker, SJ; Hicks, TJ; Goossens, DJ; Mulders, AM; Fied, Y; Yu, DH; Kennedy, SJ
    CeCu6 is a heavy Fermion compound in which the Ce magnetic moment is suppressed by the Kondo effect resulting from the admixture of the local 4f electrons with the conduction electrons. Crystal field transitions between the low-lying states of the Ce ion have been observed using inelastic neutron scattering [1–3]. The transitions were contaminated by phonon scattering which can be corrected using a complex scaling function using a complementary spectrum of LaCu6. Neutron time of flight spectroscopy with neutron polarisation analysis permits the in situ separation of magnetic and lattice vibrational energy spectra. Preliminary experiments on LONGPOL allow an indicative separation of a broadened crystal field transition and features due to lattice vibrations [4]. The preliminary analysis indicated an inelastic spin-flip feature at -12 meV which is due to the crystal field while an inelastic non-spin-flip feature at -6 meV is predominantly due to phonon scattering. A more complete polarisation analysis study has been performed using a magnetic coil to switch the polarisation at the sample position between perpendicular and parallel to the scattering vector. These results and their interpretation are reported here.
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    Single-crystal and powder neutron diffraction experiments on FePS3: search for the magnetic structure
    (American Physical Society, 2007-10) Rule, KC; McIntyre, GJ; Kennedy, SJ; Hicks, TJ
    The long-accepted magnetic structure of FePS3 has recently been refuted through extensive powder neutron diffraction studies. Single-crystal neutron diffraction, using both quasi-Laue and monochromatic techniques, has now been conducted to reveal more information about the nature of the magnetic ordering in this compound. The magnetic unit cell was found to be twice as large as the crystallographic cell in both the α and ь directions and around three times as large along the с direction, giving a propagation vector of [1/2 1/2 0.34]. There is incomplete long-range magnetic order along the c* direction due to weak Fe-Fe interactions and large anisotropy in that direction. The variation of the spontaneous moment with temperature closely resembles that for an antiferromagnetic two-dimensional Ising model on a honeycomb lattice. © 2007, American Physical Society
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    Spin glass behaviour in (Mn,Mg)S
    (Australian and New Zealand Institutes of Physics, 1994-02-09) Etheridge, GT; Kennedy, SJ; Hicks, TJ
    MnS and MgS form a solid solution with the NaCl structure. MnS is antiferromagnetic with first neighbour antiferromagnetic interactions which can never be fully satisfied because in the fcc lattice of the Mn cations first neighbours have mutual first neighbours. This competing interaction condition can lead to spin glass behaviour in a system disordered on the cation lattice. We present magnetic susceptibility and neutron powder diffraction data which suggest that with the addition of MgS to MnS, to produce a disordered cation lattice, the antiferromagnetic phase may have a reentrant spin glass phase at low temperatures and that certainly at the composition Mn0 3SMg0 63S the material is a classic spin glass.
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    Two dimensional antiferromagnetic ordering in MnPS3
    (Australian and New Zealand Institutes of Physics, 1994-02-09) Wildes, AR; Kennedy, SJ; Hicks, TJ
    MnPS3 with space group C— has a layered monoclinic structure. Within the layers the manganese atoms form a hexagonal net with each manganese atom having three manganese neighbours within the layer. Below 80K the magnetic structure is three dimensional with the antiferromagnetic ordering within the layers coupled ferromagnetically between the layers and the moment direction perpendicular to the layers. We report the discovery of a truly two dimensional antiferromagnetic ordering in the temperature range 80-130K. This order is not immediately obvious from a neutron powder diffraction pattern as the antiferromagnetic intensity appears as rods rather than spots in reciprocal space and is therefore smeared out in a powder pattern. Preliminary analysis indicates that the moment in the two dimensional structure lies in the layer plane. If this is so it would have to result from a unidirectional rather than planar anisotropy so that the system is described within the Ising model, the only model which will sustain long range magnetic order in two dimensions. The neutron diffraction data at various temperatures will be presented along with supporting single crystal susceptibility measurements.