Andrew Boothroyd: Publications

Textbook

Principles of Neutron Scattering from Condensed Matter

Published by Oxford University Press in July 2020

Temperature evolution of the magnetic excitations in charge ordered La5/3Sr1/3NiO4

JOURNAL OF PHYSICS-CONDENSED MATTER IoP Publishing Ltd 20:10 (2008) 104229

Authors:

PG Freeman, AT Boothroyd, RA Ewings, M Hucker, D Prabhakaran, M Enderle, JM Tranquada

Abstract:

Polarized- and unpolarized-neutron scattering was used to study the temperature evolution of the magnetic excitations of charge ordered La5/3Sr1/3NiO4. We studied two features in detail: (i) the resonance-like scattering at 27 meV in the quasi-two-dimensional magnetic excitations from the ordered Ni2+ (S = 1) spins, and (ii) the diffuse scattering associated with quasi-one-dimensional antiferromagnetic correlations along the stripes. Although both these features persist up to at least similar to 125 K, their temperature dependences are found to be quite different. We argue from the results that the resonance- like feature observed in La2-xSrxNiO4 (x similar to 1/3) is not caused by a coupling between the spin dynamics of the two magnetic sub-systems.

Crystal-to-stripe reordering of sodium ions in NaxCoO2 (x>=0.75)

(2008)

Authors:

DJP Morris, M Roger, MJ Gutmann, JP Goff, DA Tennant, D Prabhakaran, AT Boothroyd, E Dudzik, R Feyerherm, J-U Hoffmann, K Kiefer

Investigation of the spin state of Co in LaCo O3 at room temperature: Ab initio calculations and high-resolution photoemission spectroscopy of single crystals

Physical Review B - Condensed Matter and Materials Physics 77:4 (2008)

Authors:

SK Pandey, A Kumar, S Patil, VRR Medicherla, RS Singh, K Maiti, D Prabhakaran, AT Boothroyd, AV Pimpale

Abstract:

We investigate the spin state of LaCo O3 using state-of-the-art photoemission spectroscopy and ab initio band structure calculations. The GGA+U calculations provide a good description of the ground state for the experimentally estimated value of electron correlation strength U. In addition to the correlation effect, spin-orbit interaction is observed to play a significant role in the case of intermediate spin and high spin configurations. The comparison of the calculated Co 3d and O 2p partial density of states with the experimental valence band spectra indicates that at room temperature, Co has dominant intermediate spin state configuration and that the contribution from high spin configuration may not be significant at this temperature. The line shape of the La 5p and O 2s core level spectra could be reproduced well within these ab initio calculations. © 2008 The American Physical Society.

X-ray resonant diffraction study of multiferroic DyMn₂O₅

PHYSICAL REVIEW B 77:10 (2008) ARTN 104415

Authors:

RA Ewings, AT Boothroyd, DF McMorrow, D Mannix, HC Walker, BMR Wanklyn

Terahertz-frequency conductivity of charge stripes in the antiferromagnet La5/3Sr1/3NiO4

Irmmw Thz2007 Conference Digest of the Joint 32nd International Conference on Infrared and Millimetre Waves and 15th International Conference on Terahertz Electronics (2007) 869-870

Authors:

J Lloyd-Hughes, D Prabhakaran, E Castro-Camus, AT Boothroyd, MB Johnston

Abstract:

We report the complex refractive index of La5/3Sr 1/3NiO4 over the terahertz frequency range, obtained using time-domain spectroscopy. Negligible change in the complex refractive index with magnetic flux densities up to 6 T was seen, while changes were observed as the lattice temperature was increased from 1.5K to the charge-ordering temperature at 220 K. The terahertz frequency response therefore originates from the dielectric function rather than the magnetic permeability.

51��