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Topological constraints and ordering in model frustrated magnets / Contraintes topologiques et ordre dans les systèmes modèle pour le magnétisme frustré

Harman-Clarke, A.; (2012) Topological constraints and ordering in model frustrated magnets / Contraintes topologiques et ordre dans les systèmes modèle pour le magnétisme frustré. Doctoral thesis, UCL (University College London). Green open access

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Abstract

In this thesis a series of model frustrated magnets have been investigated. Their common parent is the spin ice model, which is transformed into the kagome ice and square ice models in two-dimensions, and an Ising spin chain model in one-dimension. These models have been examined with particular interest in the spin ordering transitions induced by constraints on the system: a topological constraint leads, under appropriate conditions, to the Kasteleyn transition in kagome ice and a lattice freezing transition is observed in square ice which is due to a ferromagnetic ordering transition in an Ising chain induced solely by finite size effects. In all cases detailed Monte Carlo computational simulations have been carried out and compared with theoretical expressions to determine the characteristics of these transitions. In order to correctly simulate the kagome ice model a loop update algorithm has been developed which is compatible with the topological constraints in the system and permits the simulation to remain strictly on the groundstate manifold within the appropriate topological sector of the phase space. A thorough survey of the thermodynamic and neutron scattering response of the kagome ice model influenced by an arbitrary in-plane field has led to a deeper understanding of the Kasteleyn transition, and a computational model that can predict neutron scattering patterns for kagome ice materials under any experimental conditions. This model has also been shown to exhibit quantised thermodynamic properties under appropriate conditions and should provide a fertile testing ground for future work on the consequences of topological constraints and topological phase transitions. A combined investigation into the square ice and Ising chain models has revealed ordering behaviour within the lattice that may be decoupled from underlying ferromagnetic ordering and is particularly relevant to magnetic nanoarrays.

Type:Thesis (Doctoral)
Title:Topological constraints and ordering in model frustrated magnets / Contraintes topologiques et ordre dans les systèmes modèle pour le magnétisme frustré
Open access status:An open access version is available from UCL Discovery
Language:English
UCL classification:UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Chemistry

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