Critical phenomena in a highly constrained classical spin system: Néel ordering from the Coulomb phaseT. 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
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.
64.70.-p - Specific phase transitions.
75.10.Hk - Classical spin models.
05.70.Jk - Critical point phenomena.
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