Title: MICROSCOPIC ANALOGUE OF THE LANDAU FREE ENERGY FOR THREE-DIMENSIONAL ISING-LIKE SYSTEMS
Author(s): M.P.Kozlovskii, I.V.Pylyuk, O.O.Prytula (Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine)

A microscopic analogue of the Landau free energy for a three-dimensional one-component spin system is found below the critical temperature as a result of direct calculations. The obtained explicit expressions make it possible to analyse the dependence of coefficients of the analogue on temperature and microscopic parameters of the system. In contrast to the case for the Landau theory, the temperature dependence of these coefficients is nonanalytic. The quantities determining the coefficients in the expression for a microscopic analogue of the Landau free energy as well as the temperature-dependence curves for the order parameter of the system are given for different values of the effective radius of the exponentially decreasing interaction potential.

Key words: Ising-like system, collective variables, Landau free energy, order parameter
PACS: 05.50.+q, 64.60.Fr, 75.10.Hk