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

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 exchangestriction model together with the Ising model for the behavior of magnetic localized 5f electrons and itinerant electrons of uranium correctly reproduces the main features of our magnetoacoustic 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 secondorder branch of the phase transition boundary as a manifestation of the tricritical fluctuations, 1