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Previous issue date: 2015-07-15 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Neste trabalho investigamos o efeito dos campos aleat?rios no modelo Blume-Capel com intera??es de longo alcance. O modelo ? completamente sol?vel no ensemble can?nico, e sua densidade de energia livre nos leva a resultados correspondentes a uma teoria de campo m?dio. S?o estudados os casos para spin S = 1 sob influ?ncia de desordem temperada na presen?a de: (i) um campo cristalino aleat?rio; (ii) de um campo magn?tico aleat?rio; (iii) e de ambos. Para uma escolha adequada do campo aleat?rio, mostramos que o modelo apresenta uma variedade de comportamentos multicr?ticos, linhas de transi??o cont?nuas e de primeira ordem, al?m de fen?menos de re-entr?ncia. Os diagramas de fases, obtidos a partir do c?lculo da energia livre por spin, exibem diversas topologias em fun??o do par?metro que mede o grau de desordem. / In the presente work we investigate the ferromagnetic Blume-Capel (BC)
model, for spin 1 and infinite-ranged interactions, under the influence of local
quenched disorder. The model is exactly solved within the canonical ensemble. The
obtained free energy density lead us to mean-field results. In the first part we study
the BC model under the influence of a random crystal-field anisotropy, but otherwise
without a magnetic field. In the second part we consider the BC model under a
bimodal random magnetic field and a uniform crystal-field anisotropy term. This
model was previously studied by Kaufman and Kanner. We give special attention
to anisotropy versus temperature phase diagrams which may present reentrant
phenomena. Finally, in the third part we consider a generalized version where both
local fields - magnetic and crystal-field anisotropy - are diluted and, in the present
case, modeled by discrete probability distribution. The phase diagram obtained and
presented in this work exhibit a rich variety of multicritical behavior, presenting
both continuous and first-order transition lines. Also, for some specific cases there is
room for the existence of reentrant effects. This seems to be a characteristic of the
Blume-Capel model under the presence of randomness.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/20402 |
| Date | 15 July 2015 |
| Creators | Santos, Priscila Vald?nia dos |
| Contributors | 27023320482, http://lattes.cnpq.br/5307397723573993, Brito, Francisco de Assis de, 75992752404, http://lattes.cnpq.br/4294161599213457, Queiroz J?nior, Idalmir de Souza, 63510731468, http://lattes.cnpq.br/8047604543096116, Silva, Luciano Rodrigues da, 07416407400, http://lattes.cnpq.br/5182830756789229, Ara?jo, Jo?o Medeiros de, Costa, Francisco Alexandre da |
| Publisher | Universidade Federal do Rio Grande do Norte, PROGRAMA DE P?S-GRADUA??O EM F?SICA, UFRN, Brasil |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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