Tricritical fluctuations and elastic properties of the Ising antiferromagnet UIrSi$_3$

TL;DR

This study investigates the elastic and magnetic properties of UIrSi$_3$, revealing tricritical fluctuations and confirming the 3D Ising model with a crossover to mean-field tricritical behavior near the phase transition.

Contribution

The paper combines experimental measurements with theoretical modeling to elucidate the role of tricritical fluctuations and elastic properties in UIrSi$_3$, advancing understanding of its phase transition behavior.

Findings

Elastic properties are mainly affected by changes in elastic modulus.

Heat capacity anomalies indicate tricritical fluctuations.

Behavior conforms to the 3D Ising model with a crossover near the tricritical point.

Abstract

Elastic constants, thermal expansion, magnetostriction and heat capacity measurements were performed with and without applied magnetic field on a single crystal of UIrSi$_3$. The elastic properties were interpreted within the theory of the strain-exchange effect. The exchange-striction model together with the Ising model for the behavior of magnetic localized 5$f$ electrons and itinerant electrons of uranium correctly reproduces the main features of our magneto-acoustic experiments in UIrSi$_3$. Data on thermal expansion and magnetostriction confirm the conclusion that the dominant contribution of the measured temperature and field change in the speed of sound comes from the change in the elastic modulus itself. Based on the analysis of heat capacity measurements in the magnetic field, we explain the significant anomalies at the second-order branch of the phase transition boundary as a manifestation of the tricritical fluctuations, dominating the region below the tricritical point. The outcome confirms the 3D Ising model, at zero and low magnetic fields, with a crossover to the mean-field tricritical behavior at fields close to the tricritical point, where tricritical fluctuations dominate the temperature evolution of the given property.