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Distinct Magnetic Phase Transition at the Surface of an Antiferromagnet

Langridge, S.; Watson, G. M.; Gibbs, D.; Betouras, J.J.; Gidopoulos, N.I.; Pollmann, F.; Long, M.W.; Vettier, C.; Lander, G.H.

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S. Langridge

G. M. Watson

D. Gibbs

J.J. Betouras

F. Pollmann

M.W. Long

C. Vettier

G.H. Lander


In the majority of magnetic systems the surface is required to order at the same temperature as the bulk. In the present Letter, we report a distinct and unexpected surface magnetic phase transition at a lower temperature than the Néel temperature. Employing grazing incidence x-ray resonant magnetic scattering, we have observed the near-surface behavior of uranium dioxide. UO2 is a noncollinear, triple-q, antiferromagnet with the U ions on a face-centered cubic lattice. Theoretical investigations establish that at the surface the energy increase—due to the lost bonds—is reduced when the spins near the surface rotate, gradually losing their component normal to the surface. At the surface the lowest-energy spin configuration has a double-q (planar) structure. With increasing temperature, thermal fluctuations saturate the in-plane crystal field anisotropy at the surface, leading to soft excitations that have ferromagnetic XY character and are decoupled from the bulk. The structure factor of a finite two-dimensional XY model fits the experimental data well for several orders of magnitude of the scattered intensity. Our results support a distinct magnetic transition at the surface in the Kosterlitz-Thouless universality class.


Langridge, S., Watson, G., Gibbs, D., Betouras, J., Gidopoulos, N., Pollmann, F., …Lander, G. (2014). Distinct Magnetic Phase Transition at the Surface of an Antiferromagnet. Physical Review Letters, 112(16), Article 167201.

Journal Article Type Article
Acceptance Date Dec 10, 2013
Online Publication Date Apr 22, 2014
Publication Date Apr 22, 2014
Deposit Date Sep 26, 2014
Publicly Available Date Oct 2, 2014
Journal Physical Review Letters
Print ISSN 0031-9007
Electronic ISSN 1079-7114
Publisher American Physical Society
Peer Reviewed Peer Reviewed
Volume 112
Issue 16
Article Number 167201
Public URL
Related Public URLs


Published Journal Article (438 Kb)

Copyright Statement
Reprinted with permission from the American Physical Society: Physical Review Letters 112, 167201 © 2014 by the American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society.

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