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Abstract: We study geometrically frustrated antiferromagnets with magnetoelasticcoupling. Frustration in these systems may be relieved by a structuraltransition to a low temperature phase with reduced lattice symmetry. We examinethe statistical mechanics of this transition and the effects on it of quencheddisorder, using Monte Carlo simulations of the classical Heisenberg model onthe pyrochlore lattice with coupling to uniform lattice distortions. The modelhas a transition between a cubic, paramagnetic high-temperature phase and atetragonal, Neel ordered low-temperature phase. It does not support thespin-Peierls phase, which is predicted as an additional possibility withinLandau theory, and the transition is first-order for reasons unconnected withthe symmetry analysis of Landau theory. Quenched disorder stabilises the cubicphase, and we find a phase diagram as a function of temperature and disorderstrength similar to that observed in ZnCdCrO.



Author: Timothy E. Saunders, John T. Chalker

Source: https://arxiv.org/







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