Issue
EPL
Volume 84, Number 3, November 2008
Article Number 36002
Number of page(s) 5
Section Condensed Matter: Structural, Mechanical and Thermal Properties
DOI http://dx.doi.org/10.1209/0295-5075/84/36002
Published online 14 October 2008
EPL, 84 (2008) 36002
DOI: 10.1209/0295-5075/84/36002

Critical phenomena in a highly constrained classical spin system: Néel ordering from the Coulomb phase

T. S. Pickles, T. E. Saunders and J. T. Chalker

Theoretical Physics, University of Oxford - 1 Keble Road, Oxford, OX1 3NP, UK


received 25 July 2008; accepted in final form 16 September 2008; published November 2008
published online 14 October 2008

Abstract
Many classical, geometrically frustrated antiferromagnets have macroscopically degenerate ground states. In a class of three-dimensional systems, the set of degenerate ground states has power law correlations and is an example of a Coulomb phase. We investigate Néel ordering from such a Coulomb phase, induced by weak additional interactions that lift the degeneracy. We show that the critical point belongs to a universality class that is different from the one for the equivalent transition out of the paramagnetic phase, and instead that this transition is characterised by effective long-range interactions; alternatively, ordering may be discontinuous. We suggest that a transition of this type may be realised by applying uniaxial stress to a pyrochlore antiferromagnet.

PACS
64.70.-p - Specific phase transitions.
75.10.Hk - Classical spin models.
05.70.Jk - Critical point phenomena.

© EPLA 2008