Browsing by Author "Ehlers, G"

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    Dynamics of linarite: observations of magnetic excitations
    (American Physical Society, 2017-01-26) Rule, KC; Willenberg, B; Schäpers, M; Wolter, AUB; Büchner, B; Drechsler, SL; Ehlers, G; Tennant, DA; Mole, RA; Gardner, JS; Süllow, S; Nishimoto, S
    Here we present inelastic neutron scattering measurements from the frustrated, quantum spin-1/2 chain material linarite, PbCuSO4(OH)2. Time of flight data, taken at 0.5 K and zero applied magnetic field reveals low-energy dispersive spin wave excitations below 1.5 meV both parallel and perpendicular to the Cu-chain direction. From this we confirm that the interchain couplings within linarite are around 10% of the nearest neighbor intrachain interactions. We analyze the data within both linear spin-wave theory and density matrix renormalization group theories and establish the main magnetic exchange interactions and the simplest realistic Hamiltonian for this material. ©2017 American Physical Society.
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    Inelastic neutron scattering as a means for determining the magnetic exchange interactions in the frustrated quantum spin chain, Linarite
    (Australian Institute of Physics, 2021-02-02) Rule, KC; Willenberg, B; Mole, RA; Wolter-Giraud, A; Tennant, A; Ehlers, G; Studer, AJ; Gardner, J; Suellow, S
    One of the simplest models exhibiting one dimensional (1D) frustrated quantum interactions is the so called J1-J2 model. In this model competing ferromagnetic nearest-neighbour interactions (J1 > 0) and antiferromagnetic next-nearest-neighbours (J2 < 0) can give rise to novel phenomena such as multiferroicity for spiral spin states. Linarite, PbCuSO4(OH)2 is a natural mineral ideally suited to the study of frustration in J1-J2 systems due to an accessible saturation field and the availability of large single crystals well suited to neutron investigations. In this material the Cu2+ ions form spin S = 1/2 chains along the b direction with dominant nearest-neighbour FM interactions and a weaker next-nearest-neighbour AFM coupling, resulting in a magnetically frustrated topology. We present a neutron scattering study of linarite revealing a helical magnetic ground state structure with an incommensurate propagation vector of (0, 0.186, ½) below TN = 2.8K in zero magnetic field. From detailed measurements in magnetic fields up to 12 T (B || b), a very rich magnetic phase diagram will be presented. In particular we will present new inelastic neutron scattering data and compare this with theoretical modelling of the spin Hamiltonian. These theoretical calculations imply that linarite possesses an xyz exchange anisotropy. Our data establish linarite as a model compound of the frustrated one-dimensional spin chain, with ferromagnetic nearest-neighbour and antiferromagnetic next-nearest-neighbour interactions.
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    Low energy spin dynamics in the spin ice Ho2Sn2O7
    (Intitite of Physics Publishing Ltd, 2012-02-22) Ehlers, G; Huq, A; Diallo, SO; Adriano, C; Rule, KC; Cornelius, AL; Fouquet, P; Pagliuso, PG; Gardner, JS
    The magnetic properties of Ho 2 Sn 2 O 7 have been investigated and compared to other spin ice compounds. Although the lattice has expanded by 3% relative to the better studied Ho 2 Ti 2 O 7 spin ice, no significant changes were observed in the high temperature properties, T greater than or similar to 20 K. As the temperature is lowered and correlations develop, Ho 2 Sn 2 O 7 enters its quantum phase at a slightly higher temperature than Ho 2 Ti 2 O 7 and is more antiferromagnetic in character. Below 80 K a weak inelastic mode associated with the holmium nuclear spin system has been measured. The hyperfine field at the holmium nucleus was found to be ≈700 T. (c) 2012 IOP Publishing LTD