Efeito da ordem de curto-alcance em magnetismo e outros fenomenos cooperativos

AUTOR(ES)
DATA DE PUBLICAÇÃO

1984

RESUMO

The order-disorder transformation for the Ising model with spin 1/2 is studied in relation to several problems in the area of cooperative phenomena. All those problems can be described by a two-state model and correspondingly mapped onto the Ising model, their critical behavior having universal properties no matter the details of the interaction. Correlation effects in the disordered phase lead to short-range order a fact not accounted for by the classical molecular field theory but responsible of several important observed properties. Multi-site correlations can be progressively included into the theory by means of the cluster-variation method developed by Kikuchi for order-disorder transformations. In particular. the paramagnetic susceptibility for an Ising system is studied, taking into account those effects related to short-range order. An exact result for the resonance frequencies of an Ising system is obtained using the Green function formalism developed by Zubarev. A first order phase transition can also be accounted for with the same model following the procedure of Lee and Yang for the lattice gas. The solid-fluid transition for a bidimensional system is studied in close analogy with a magnetic system, the latent heat of the transition giving origin to a temperature dependent effective magnetic field, when the natural isomorphism with the magnetic system is formulated. This latter model is used to study the gel-fluid transition of lipid mono and bilayers, a problem which describes fairly well the behavior of biological membranes

ASSUNTO(S)

magnetismo

ACESSO AO ARTIGO

Documentos Relacionados