Equation of State and Thermodynamic Functions of the Ising-like Magnet at $T>T_c$

TL;DR

This paper uses a non-perturbative collective variables method to analyze the equation of state and thermodynamic functions of a 3D Ising-like magnet above the critical temperature, capturing universal and nonuniversal features.

Contribution

It introduces a microscopic, non-perturbative approach to derive system characteristics across the entire critical region in the $h-T$ plane.

Findings

Susceptibility behavior near the critical point is characterized.

Locations of susceptibility maxima are identified for various fields.

Universal and nonuniversal properties are obtained from the Hamiltonian.

Abstract

The 3D Ising-like system in the external field is described using the non-perturbative collective variables method. The universal as well as nonuniversal system characteristics are obtained within the framework of this approach. The calculations are carried out on the microscopic level starting from the Hamiltonian. They are valid in the whole $h-T$ plane of the critical region. It is established, that the contributions related with wave vector values $\vk\to0$ exhibit the properties of the total system near the critical point. The behaviour of the susceptibility as function of the temperature in the presence of the field is investigated. The locations of the maximums susceptibility on the temperature scale for different values of the field are established.