Magnetoelastic properties and critical fluctuations - UIrSi$_3$ case study

Magnetoelastic properties and critical fluctuations - UIrSi$_3$ case study

T.N. HAIDAMAK, J. VALENTA, J. PRCHAL, M. VALISKA, J. PROKLESKA, J. POSPISIL,
V. SECHOVSKY$^{1}$, A.A. ZVYAGIN$^{2}$, and F. HONDA$^{3}$

$^{1}$Ke Karlovu 5, CZ-12116 Praha 2, Czech Republic (Faculty of Mathematics and Physics, Charles University, DCMP)
$^{2}$Nauki ave. 47, 61103, Kharkov, Ukraine
(B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine)
$^{3}$Motooka 744, Fukuoka-Nishi, Fukuoka 819-0395, Japan
(Central Institute of Radioisotope Science and Safety Management Kyushu University)

UIrSi$_3$ is one of the few uranium compounds to exhibit Ising like antiferromagnetism with a tricritical point in the H-T magnetic phase diagram [1,2]. The tricritical point separates the segments of first- and second-order field-induced transitions between the antiferromagnetic and paramagnetic state. Our previous study of magnetic, thermal, and transport properties supported by $ab$-initio calculation of the ground state [1,2] revealed the rich physics of this compound. To understand the relation between the magnetic and crystal structure we experimentally studied the elastic constants, thermal expansion, magnetostriction and heat capacity. 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 $U$ 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 fluctuation, 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 given property.

[1] J. Valenta, F. Honda, M. Valiska, P. Opletal, J. Kastil, M. Misek, M. Divis, L. Sandratskii, J. Prchal, and V. Sechovsky, Phys. Rev. B ${\bf 97}$, 144423 (2018).
[2] F. Honda, J. Valenta, J. Prokleska, J. Pospisil, P. Proschek, J. Prchal, and V. Sechovsky Phys. Rev. B ${\bf 100}$, 014401 (2019).

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