Browsing by Author "Wildes, AR"
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- ItemThe magnetic properties and structure of the quasi-two-dimensional antiferromagnet CoPS3(IOP Science, 2017-10-12) Wildes, AR; Simonet, V; Ressouche, E; Ballou, R; McIntyre, GJThe magnetic properties and magnetic structure are presented for CoPS3, a quasi-twodimensional antiferromagnet on a honeycomb lattice with a Néel temperature of TN ∼ 120 K. The compound is shown to have XY-like anisotropy in its susceptibility, and the anisotropy is analysed to extract crystal field parameters. For temperatures between 2K and 300K, no phase transitions were observed in the field-dependent magnetization up to 10 Tesla. Singlecrystal neutron diffraction shows that the magnetic propagation vector is k = (010) with the moments mostly along the a axis and with a small component along the c axis, which largely verifies the previously-published magnetic structure for this compound. The magnetic Bragg peak intensity decreases with increasing temperature as a power law with exponent 2β = 0.60 ± 0.01 for T > 0.9 TN. © 2017 IOP Publishing Ltd
- ItemMagnetic 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, ARNeutron 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
- ItemMagnetic 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, TJThe 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
- ItemThe magnon dynamics and spin exchange parameters of FePS3(IOP Publishing Ltd, 2012-10-17) Wildes, AR; Rule, KC; Bewley, RI; Enderle, M; Hicks, TJThe 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.
- ItemMelting of highly oriented fiber DNA subjected to osmotic pressure(ACS Publications, 2015-03-15) Wildes, AR; Khadeeva, LZ; Trewby, W; Valle-Orero, J; Studer, AJ; Garden, JL; Peyrard, MA pilot study of the possibility to investigate temperature-dependent neutron scattering from fiber-DNA in solution is presented. The study aims to establish the feasibility of experiments to probe the influence of spatial confinement on the structural correlation and the formation of denatured bubbles in DNA during the melting transition. Calorimetry and neutron scattering experiments on fiber samples immersed in solutions of poly(ethylene glycol) (PEG) prove that the melting transition occurs in these samples, that the transition is reversible to some degree, and that the transition is broader in temperature than for humidified fiber samples. The PEG solutions apply an osmotic pressure that maintains the fiber orientation, establishing the feasibility of future scattering experiments to study the melting transition in these samples. © 2015 American Chemical Society
- ItemThermal denaturation of A-DNA(IOP Science, 2014-11-07) Valle-Orero, J; Wildes, AR; Theodorakopoulos, N; Cuesta-López, S; Garden, JL; Danilkin, SA; Peyrard, MThe DNA molecule can take various conformational forms. Investigations focus mainly on the so-called 'B-form', schematically drawn in the famous paper by Watson and Crick [1]. This is the usual form of DNA in a biological environment and is the only form that is stable in an aqueous environment. Other forms, however, can teach us much about DNA. They have the same nucleotide base pairs for 'building blocks' as B-DNA, but with different relative positions, and studying these forms gives insight into the interactions between elements under conditions far from equilibrium in the B-form. Studying the thermal denaturation is particularly interesting because it provides a direct probe of those interactions which control the growth of the fluctuations when the 'melting' temperature is approached. Here we report such a study on the 'A-form' using calorimetry and neutron scattering. We show that it can be carried further than a similar study on B-DNA, requiring the improvement of thermodynamic models for DNA.© 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
- ItemTwo dimensional antiferromagnetic ordering in MnPS3(Australian and New Zealand Institutes of Physics, 1994-02-09) Wildes, AR; Kennedy, SJ; Hicks, TJMnPS3 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.