Zeros de Fisher e aspectos críticos do modelo de Ising dipolar / Fisher\ s zeros and critical aspects of the dipolar Ising model

AUTOR(ES)

Jacyana Saraiva Marthes Fonseca

FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

06/06/2011

RESUMO

We study the critical behavior of the dipolar Ising model on two-dimensional regular lattices. This model presents a phenomenologically rich scenario due to the effect of frustration caused by the competition between the pure Ising interaction and the dipolar one. To study the criticality of this model we apply finite size scaling relations for the partition function zeros in the complex temperature plane. The partition function zeros analysis has never been used before to study such model with long-range interactions. Our study relies on Monte Carlo simulations using the multicanonical algorithm. Our goal is to obtain the critical temperature as a function of the coupling (the ratio between the ferromagnetic and dipolar couplings) to construct a part of the phase diagram. Different parts of the phase diagram do not present a conclusive results about the order of the phase transition lines.In particular, there is evidence of a tricritical point for [0.90,1.00], but its precise location is unknown. Our simulations indicate that the tricritical point is not located in the above range. Our FSS analysis show that for =1.20 the striped-tetragonal transition is a second-order phase transition and for =1.30 it is a first-order one. Thus, the tricritical point must occur between =1.2 and =1.3. We have used a microcanonical approach to study the criticality of this model too. This approach indicates two second-order phase transitions for =1.20 and two first-order phase transitions for =1.30. Therefore, it presents evidences for the presence of an intermediate nematic phase.

ASSUNTO(S)

multicanonical algorithm phase transitions transições de fase zeros complexos da função de partição algoritmo multicanônico complex zeros of the partition function dipolar ising model modelo de ising dipolar

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