X-ray and neutron scattering

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Nature of the magnetic order and origin of induced ferroelectricity in TbMnO3

Physical Review Letters 103:20 (2009)

Authors:

SB Wilkins, TR Forrest, TAW Beale, SR Bland, HC Walker, D Mannix, F Yakhou, D Prabhakaran, AT Boothroyd, JP Hill, PD Hatton, DF McMorrow

Abstract:

The magnetic structures which endow TbMnO3 with its multiferroic properties have been reassessed on the basis of a comprehensive soft x-ray resonant scattering (XRS) study. The selectivity of XRS facilitated separation of the various contributions (Mn L2 edge, Mn 3d moments; Tb M4 edge, Tb 4f moments), while its variation with azimuth provided information on the moment direction of distinct Fourier components. When the data are combined with a detailed group theory analysis, a new picture emerges of the ferroelectric transition at 28 K. Instead of being driven by the transition from a collinear to a noncollinear magnetic structure, as has previously been supposed, it is shown to occur between two noncollinear structures. © 2009 The American Physical Society.
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High-resolution hard x-ray photoemission investigation of La 2-2xSr 1+2xMn 2O 7 (0.30≤x<0.50): Microscopic phase separation and surface electronic structure of a bilayer colossal magnetoresistance manganite

Physical Review B - Condensed Matter and Materials Physics 80:20 (2009)

Authors:

S De Jong, F Massee, Y Huang, M Gorgoi, F Schaefers, J Fink, AT Boothroyd, D Prabhakaran, JB Goedkoop, MS Golden

Abstract:

Photoemission data taken with hard x-ray radiation on cleaved single crystals of the bilayered, colossal magnetoresistant manganite La 2-2xSr 1+2xMn 2O 7 (LSMO) with 0.30≤x<0.50 are presented. Making use of the increased bulk sensitivity upon hard x-ray excitation it is shown that the core-level footprint of the electronic structure of the LSMO cleavage surface is identical to that of the bulk. Furthermore, by comparing the core-level shift of the different elements as a function of doping level x, it is shown that microscopic phase separation is unlikely to occur for this particular manganite well above the Curie temperature. © 2009 The American Physical Society.
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Nonlinear Optical Properties and Ferroelectric Phase Transition of LaBGeO5

Ferroelectrics Taylor & Francis 389:1 (2009) 125-131

Authors:

Hiroko Yokota, Yoshiaki Uesu, Boris Strukov, Michael Glazer
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Inward dispersion of the spin excitation spectrum of stripe-ordered La2NiO4+d

(2009)

Authors:

PG Freeman, SM Hayden, CD Frost, M Enderle, DX Yao, EW Carlson, D Prabhakaran, AT Boothroyd
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Magnetic Coulomb phase in the spin ice Ho2Ti2O7.

Science 326:5951 (2009) 415-417

Authors:

T 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. Their low-temperature magnetic state has been predicted to be a phase that obeys a Gauss' law and supports magnetic monopole excitations: in short, a Coulomb phase. We used polarized neutron scattering to show that the spin-ice material Ho2Ti2O7 exhibits an almost perfect Coulomb phase. Our result proves the existence of such phases in magnetic materials and strongly supports the magnetic monopole theory of spin ice.
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