Description of critical behavior of Ising ferromagnet in the ρ6 model approximation taking into account confluent correction. I. Region above the phase transition point

Abstract

The behavior of a 3D Ising system at temperatures above Tc is studied in the approximation of sextic distribution for modes of spin moment density oscillations (ρ6 model). An original method is developed in this higher non-Gaussian approximation for calculating the thermodynamic characteristics of the 3D Ising model near Tc taking into account the first confluent correction. The contributions to the thermodynamic functions of an Ising ferromagnet (free energy, entropy, internal energy, and specific heat) from the short-wave and long-wave modes of spin density oscillations are considered separately. A nonuniversal factor determined by microscopic characteristics of the system is singled out in the expressions for leading critical amplitudes and the amplitudes of the confluent correction. Numerical estimates of the critical region size, phase transition temperature, leading critical amplitudes, and the amplitudes of the correction to scaling of specific heat and susceptibility of the system are given for different values of effective radius of the exponentially decreasing interaction potential.