X-ray and neutron scattering

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Magnetic order and dynamics of the charge-ordered antiferromagnet La1.5Sr0.5CoO4

(2009)

Authors:

LM Helme, AT Boothroyd, R Coldea, D Prabhakaran, CD Frost, DA Keen, LP Regnault, PG Freeman, M Enderle, J Kulda
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Topologically Ordered Amorphous Silica Obtained from the Collapsed Siliceous Zeolite, Silicalite-1-F: A Step toward “Perfect” Glasses

Journal of the American Chemical Society American Chemical Society (ACS) 131:34 (2009) 12333-12338

Authors:

Julien Haines, Claire Levelut, Aude Isambert, Philippe Hébert, Shinji Kohara, David A Keen, Tahar Hammouda, Denis Andrault
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Ultrafast coupling between light, coherent lattice vibrations, and the magnetic structure of semicovalent LaMnO(3).

Phys Rev Lett 103:9 (2009) 097402

Authors:

S Wall, D Prabhakaran, AT Boothroyd, A Cavalleri

Abstract:

Coherent lattice vibrations are excited and probed with pulses of 10 fs duration in LaMnO(3). The measured frequencies correspond to those of Jahn-Teller stretching and of out-of phase rotations of the oxygen octahedra. Surprisingly, the amplitude and damping rate of both modes exhibit a sharp discontinuity at the Néel temperature, highlighting nontrivial coupling between light, lattice, and magnetic structure. We explain this effect by applying the Goodenough-Kanamori rules to the excited state of LaMnO(3), and note that charge transfer can invert the sign of the semicovalent exchange interaction, which in turn perturbs the equilibrium bond lengths.
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Coexistence of incommensurate magnetism and superconductivity in Fe_{1+y}Se_xTe_{1-x}

(2009)

Authors:

R Khasanov, M Bendele, A Amato, P Babkevich, AT Boothroyd, A Cervellino, K Conder, SN Gvasaliya, H Keller, H-H Klauss, H Luetkens, E Pomjakushina, B Roessli
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Experimental Proof of a Magnetic Coulomb Phase

ArXiv 0907.0954 (2009)

Authors:

Tom Fennell, PP Deen, AR Wildes, K Schmalzl, D Prabhakaran, AT Boothroyd, RJ Aldus, DF McMorrow, ST Bramwell

Abstract:

Spin ice materials are magnetic substances in which the spin directions map onto hydrogen positions in water ice. Recently this analogy has been elevated to an electromagnetic equivalence, indicating that the spin ice state is a Coulomb phase, with magnetic monopole excitations analogous to ice's mobile ionic defects. No Coulomb phase has yet been proved in a real magnetic material, as the key experimental signature is difficult to resolve in most systems. Here we measure the scattering of polarised neutrons from the prototypical spin ice Ho2Ti2O7. This enables us to separate different contributions to the magnetic correlations to clearly demonstrate the existence of an almost perfect Coulomb phase in this material. The temperature dependence of the scattering is consistent with the existence of deconfined magnetic monopoles connected by Dirac strings of divergent length.
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