Ground state structure, domain walls, and external field response in random magnets

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dc.contributor Aalto-yliopisto fi
dc.contributor Aalto University en
dc.contributor.author Seppälä, Eira
dc.date.accessioned 2012-02-13T12:22:44Z
dc.date.available 2012-02-13T12:22:44Z
dc.date.issued 2001-05-25
dc.identifier.isbn 951-22-5459-X
dc.identifier.issn 1455-1802
dc.identifier.uri https://aaltodoc.aalto.fi/handle/123456789/2336
dc.description.abstract The ground state structure and domain walls in Ising-like magnets with quenched randomness are studied at zero temperature. The methods employed are exact ground state calculations using graph-theoretical optimization and extreme statistics arguments. The elastic manifolds, i.e., domain walls, with random-bond disorder are investigated with two different types of periodicity. The first type of periodicity is when the randomness is periodically repeated. It is shown to lead after a cross-over to the periodic elastic media universality class, whenever the period lambda is finite. The second periodicity is due to an additional modulating potential. There are two types of intermittence seen before the asymptotic random-bond roughness behavior is reached. The first type is when the manifolds jump between the minima of the periodic potential and the second type is when the interfaces roughen over pinning energy barriers. An external field is applied to the random manifolds. An energy minimization argument based on the glassy energy landscape indicates that in an equilibrium system the manifolds move by sharp jumps between nearly degenerate energy minima in analogy to a first-order transition. A mean field argument for the finite-size scaling of the first jump field is derived and numerically confirmed. Using extreme statistics and probabilistic arguments, the probability distribution of the first jump field and its finite size scaling are calculated. Based on these the susceptibility of the manifolds is derived. Random field magnets are studied in two dimensions. The break-up of long-range order is shown to have a first-order character. The domain wall behavior is studied, leading to an interface scaling with a roughness exponent greater than unity below the break-up length scale. The domain wall energy is demonstrated to vanish logarithmically confirming the destruction of the long-range order. The magnetization and susceptibility versus the external field are investigated, and they show continuous behaviors and are independent of the break-up length scale. However, another long-range order, percolation, is found in two-dimensional random field magnets. The percolation transition with respect to the external field belongs to the standard short-range correlated two-dimensional percolation universality class. The whole phase diagram for percolation as a function of the random field strength and the external field is predicted. en
dc.format.extent 49, [64]
dc.format.mimetype application/pdf
dc.language.iso en en
dc.publisher Helsinki University of Technology en
dc.publisher Teknillinen korkeakoulu fi
dc.relation.ispartofseries Dissertations / Laboratory of Physics, Helsinki University of Technology en
dc.relation.ispartofseries 112 en
dc.relation.haspart E. T. Seppälä, M. J. Alava, and P. M. Duxbury, Periodic elastic medium in which periodicity is relevant, Physical Review E 62, 3230-3233 (2000). [article1.pdf] © 2000 American Physical Society. By permission.
dc.relation.haspart E. T. Seppälä, M. J. Alava, and P. M. Duxbury, Intermittence and roughening of periodic elastic media, Physical Review E 63, 036126 (2001) (7 pages). [article2.pdf] © 2001 American Physical Society. By permission.
dc.relation.haspart E. T. Seppälä and M. J. Alava, Energy landscapes in random systems, driven interfaces and wetting, Physical Review Letters 84, 3982-3985 (2000). [article3.pdf] © 2000 American Physical Society. By permission.
dc.relation.haspart E. T. Seppälä, M. J. Alava, and P. M. Duxbury, Extremal statistics in the energetics of domain walls, Physical Review E 63, 066110 (2001) (4 pages). [article4.pdf] © 2001 American Physical Society. By permission.
dc.relation.haspart E. T. Seppälä and M. J. Alava, Energy landscapes, lowest gaps, and susceptibility of elastic manifolds at zero temperature, accepted for publication in European Physical Journal B. [article5.pdf] © 2001 EDP Sciences. By permission.
dc.relation.haspart E. T. Seppälä, V. Petäjä, and M. J. Alava, Disorder, order, and domain wall roughening in the two-dimensional random field Ising model, Physical Review E 58, R5217-R5220 (1998). [article6.pdf] © 1998 American Physical Society. By permission.
dc.relation.haspart E. T. Seppälä and M. J. Alava, Susceptibility and percolation in two-dimensional random field Ising magnets, Physical Review E 63, 066109 (2001) (14 pages). [article7.pdf] © 2001 American Physical Society. By permission.
dc.subject.other Physics en
dc.title Ground state structure, domain walls, and external field response in random magnets en
dc.type G5 Artikkeliväitöskirja fi
dc.description.version reviewed en
dc.contributor.department Department of Engineering Physics and Mathematics en
dc.contributor.department Teknillisen fysiikan ja matematiikan osasto fi
dc.subject.keyword quenched randomness en
dc.subject.keyword Ising model en
dc.subject.keyword domain walls en
dc.subject.keyword optimization en
dc.subject.keyword percolation en
dc.identifier.urn urn:nbn:fi:tkk-002818
dc.type.dcmitype text en
dc.type.ontasot Väitöskirja (artikkeli) fi
dc.type.ontasot Doctoral dissertation (article-based) en
dc.contributor.lab Laboratory of Physics en
dc.contributor.lab Fysiikan laboratorio fi


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