X-ray and neutron scattering

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Circularly polarized x-ray scattering investigation of spin-lattice coupling in TbMnO3 in crossed electric and magnetic fields

Physical Review B - Condensed Matter and Materials Physics 88:21 (2013)

Authors:

HC Walker, F Fabrizi, L Paolasini, F De Bergevin, D Prabhakaran, AT Boothroyd, DF McMorrow

Abstract:

We present a study of the magnetic and crystallographic structure of TbMnO3 in the presence of crossed electric and magnetic fields using circularly polarized x-ray nonresonant scattering. A comprehensive account is presented of the scattering theory and data analysis methods used in our earlier studies, and in addition we present interesting high magnetic field data and its analysis. We discuss in detail how polarization analysis was used to reveal structural information, including the arrangement of Tb moments which we proposed for H=0 T, and how the diffraction data for HHC as for H
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Circularly Polarised X-ray Scattering Investigation of Spin-Lattice Coupling in TbMnO$_3$ in Crossed Electric and Magnetic Fields

(2013)

Authors:

HC Walker, F Fabrizi, L Paolasini, F de Bergevin, D Prabhakaran, AT Boothroyd, DF McMorrow
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A ferroelectric-like structural transition in a metal

Nature Materials 12:11 (2013) 1024-1027

Authors:

Y Shi, Y Guo, X Wang, AJ Princep, D Khalyavin, P Manuel, Y Michiue, A Sato, K Tsuda, S Yu, M Arai, Y Shirako, M Akaogi, N Wang, K Yamaura, AT Boothroyd

Abstract:

Metals cannot exhibit ferroelectricity because static internal electric fields are screened by conduction electrons, but in 1965, Anderson and Blount predicted the possibility of a ferroelectric metal, in which a ferroelectric-like structural transition occurs in the metallic state. Up to now, no clear example of such a material has been identified. Here we report on a centrosymmetric () to non-centrosymmetric (R3c) transition in metallic LiOsO 3 that is structurally equivalent to the ferroelectric transition of LiNbO 3 (ref.). The transition involves a continuous shift in the mean position of Li + ions on cooling below 140 K. Its discovery realizes the scenario described in ref., and establishes a new class of materials whose properties may differ from those of normal metals. © 2013 Macmillan Publishers Limited. All rights reserved.
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Coupling of magnetic order to planar Bi electrons in the anisotropic Dirac metals AMnBi2 (A = Sr, Ca)

(2013)

Authors:

YF Guo, AJ Princep, X Zhang, P Manuel, D Khalyavin, II Mazin, YG Shi, AT Boothroyd
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Suppression of thermal conductivity by rattling modes in thermoelectric sodium cobaltate

Nature Materials 12:11 (2013) 1028-1032

Authors:

DJ Voneshen, K Refson, E Borissenko, M Krisch, A Bosak, A Piovano, E Cemal, M Enderle, MJ Gutmann, M Hoesch, M Roger, L Gannon, AT Boothroyd, S Uthayakumar, DG Porter, JP Goff

Abstract:

The need for both high electrical conductivity and low thermal conductivity creates a design conflict for thermoelectric systems, leading to the consideration of materials with complicated crystal structures. Rattling of ions in cages results in low thermal conductivity, but understanding the mechanism through studies of the phonon dispersion using momentum-resolved spectroscopy is made difficult by the complexity of the unit cells. We have performed inelastic X-ray and neutron scattering experiments that are in remarkable agreement with our first-principles density-functional calculations of the phonon dispersion for thermoelectric Na 0.8 CoO2, which has a large-period superstructure. We have directly observed an Einstein-like rattling mode at low energy, involving large anharmonic displacements of the sodium ions inside multi-vacancy clusters. These rattling modes suppress the thermal conductivity by a factor of six compared with vacancy-free NaCoO2. Our results will guide the design of the next generation of materials for applications in solid-state refrigerators and power recovery. © 2013 Macmillan Publishers Limited. All rights reserved.
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