Critical equation of state of randomly dilute Ising systems

TL;DR

This paper determines the critical equation of state for three-dimensional randomly dilute Ising systems, providing universal amplitude ratios and comparing them with experimental data.

Contribution

It introduces a systematic approximation scheme for the equation of state in the critical regime of disordered Ising systems.

Findings

Estimated universal amplitude ratio A^+/A^- = 1.6(3)

Good agreement with experimental results on dilute uniaxial antiferromagnets

Developed polynomial parametric representations for the equation of state

Abstract

We determine the critical equation of state of three-dimensional randomly dilute Ising systems, i.e. of the random-exchange Ising universality class. We first consider the small-magnetization expansion of the Helmholtz free energy in the high-temperature phase. Then, we apply a systematic approximation scheme of the equation of state in the whole critical regime, that is based on polynomial parametric representations matching the small-magnetization of the Helmholtz free energy and satisfying a global stationarity condition. These results allow us to estimate several universal amplitude ratios, such as the ratio A^+/A^- of the specific-heat amplitudes. Our best estimate A^+/A^-=1.6(3) is in good agreement with experimental results on dilute uniaxial antiferromagnets.