Phase transitions in layered isotropic systems

Publisher Website
Google Scholar
Abstract
A theory of phase transitions for systems of weakly coupled layers with an isotropic order parameter is developed. The properties of the two-dimensional (2D) system are assumed to be known, and the interlayer coupling is treated by a mean-field or random-phase type approximation leading to an appropriate Landau-Ginzburg free-energy functional for the 3D system. The assumption that the pure 2D system has a phase transition and that it satisfies scaling is shown to lead to a number of measurable consequences. The 3D ordering temperature, the 2D-3D crossover region, the 3D critical region, and mean-field specific-heat jump as well as other mean-field properties are obtained as functions of the interlayer coupling. Comparison with existing experimental results for almost isotropic layered ferromagnets supports the existence of a finite transition temperature in 2D. However, the non-symmetry-broken low-temperature phase is found within our approximation to be unattainable owing to the finite interlayer fields.