Nova abordagem de teoria de campo efetivo aplicada ao Modelo de Ising com interações competitivas

Abstract

The research of high temperature superconducting compounds formed by plans C uO2, has motivated the theoretical study in proposing a model able to describe their characteristics. In particular, these compounds have a common antiferromagnetic ordering, that for small doping, the Ne´el temperature is drastically reduced to zero when a critical concentration is reached pc. In this work, was used the randomly antiferromagnetic Ising model decorated with spin df rac12 and competitive interactions to describe properties C uO2. This model consists of plans, in which the nodal spins interact antiferromagnetically J1 with its nearest neighbors (C u − C u interactions) and ferromagneticamente JF with the spins decorators (C u − Ointeractions) that are randomly distributed ( textit quenched) over a three-dimensional network. It used the effective field theory based on operator technique for studying the differential phase transition in a cluster formed by two sites in a cubic lattice. The system was analyzed for the almost-two- dimensional topologies and three-dimensional, initially, from the perspective of methodology Zernike, usually used in statistical mechanics, where you can analyze the phase diagram and the behavior of the magnetization. posteriorly, was applied a new methodological approach decoupling the model, which was analyzed only the phase diagram. Discussed the variation of the critical concentration pc where the Ne´el temperature tends to zero for various values of the frustration parameter α. For certain values of this parameter was observed reentrant behavior at low temperatures. Was calculated dependence of magnetization subnet as a function of temperature for analyzing the behavior observed in reentrant of phase diagrams.