Abstract
In article the study of the surface phase changes in the thin films described by the antiferromagnetic Ising model, by computer modeling is executed. The Metropolis algorithm is used. Modeling is executed at various values of exchange integrals relation on a surface and in bulk of films RS. The difference of exchange integral between the surface spins and the first subsurface layer RSB from volume value is considered. The limiting cases of the value RSB are considered. Two order parameters are used. The first order parameter defines an antiferromagnetic order in the bulk of system. It is calculated as chess magnetization of the spins located not on a surface. Its value is equal to the difference of magnet moments for two sublattices. For study of the surface phase transition, the second order parameter is entered. It is calculated as chess magnetization of the spins located on the free surface. For definition of transition temperature, bulk and surface Binder’s cummulants are used. The computer experiment for various values of film thickness from 4 to 12 layers is made. The relation of exchange integrals changed from 0.5 to 2.0. Temperatures of bulk and surface phase transition are identical at all relations of exchange integrals. Transition temperature grows at increase in the exchange integrals relation RS. Growth rate of transition temperature depends on thickness of a film and velue RSB. The difference of exchange integral between the surface layer and the first subsurface layer leads to more rapid growth of the transition temperature. For all values of exchange integrals there is a cross point for temperature curves at any thickness of a film.
Highlights
Surface magnetism is observed experimentally in both ferromagnetic and antiferromagnetic systems
The aim of this paper is to study by computer modeling the phase transitions in thin films, described by the antiferromagnetic Ising model, at different values of surface energy and values of the interaction of the surface with the subsurface layer
The order parameter m will determine the antiferromagnetic order in the main bulk of a system and will be calculated as the staggered magnetization of the spins located not on the surface
Summary
Surface magnetism is observed experimentally in both ferromagnetic and antiferromagnetic systems. It is not taken into account that the interaction between the surface spins and the first subsurface layer differs from the bulk interaction Taking this effect into consideration may have a significant influence on the phase diagram of a system and the critical-behavior regime, since the bulk of a system and the surface play the role of an external field for each other in ordering. The value of the exchange integral between the surface spins and the first subsurface layer determines the intensity of their interaction As it was shown in the paper [19] for semi-bounded antiferromagnetics, taking this effect into consideration changes the phase diagram of a system. The aim of this paper is to study by computer modeling the phase transitions in thin films, described by the antiferromagnetic Ising model, at different values of surface energy and values of the interaction of the surface with the subsurface layer
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