The nematic susceptibility of the ferroquadrupolar metal TmAg2 measured via the elastocaloric effect

TL;DR

This study measures the nematic susceptibility of TmAg2 using elastocaloric effects, revealing a Curie-Weiss behavior and the influence of magnetic fields on quadrupolar fluctuations, advancing understanding of ferroquadrupolar phase transitions.

Contribution

It introduces elastocaloric measurements as a new method to probe quadrupolar fluctuations and nematic susceptibility in TmAg2, providing insights consistent with previous elastic constant studies.

Findings

Elastocaloric effect detects ferroquadrupolar transition at 5K.

Nematic susceptibility follows Curie-Weiss law with Weiss temperature ~2.7K.

Magnetic field along c-axis acts as a transverse field for quadrupoles.

Abstract

Elastocaloric measurements of the ferroquadrupolar/nematic rare-earth intermetallic TmAg$_2$ are presented. TmAg$_2$ undergoes a cooperative Jahn-Teller-like ferroquadrupolar phase transition at 5K, in which the Tm$^{3+}$ ion's local $4f$ electronic ground state doublet spontaneously splits and develops an electric quadrupole moment which breaks the rotational symmetry of the tetragonal lattice. The elastocaloric effect, which is the temperature change in the sample induced by adiabatic strains the sample experiences, is sensitive to quadrupolar fluctuations in the paranematic phase which couple to the induced strain. We show that elastocaloric measurements of this material reveal a Curie-Weiss like nematic susceptibility with a Weiss temperature of $\approx 2.7K$, in agreement with previous elastic constant measurements. Furthermore, we establish that a magnetic field along the c-axis acts as an effective transverse field for the quadrupole moments.