Giant elastocaloric effect at low temperatures in TmVO$_4$ and implications for cryogenic cooling

TL;DR

This study demonstrates the giant elastocaloric effect in TmVO$_4$ at low temperatures, highlighting its potential for cryogenic cooling through strain-induced entropy changes near a quadrupolar phase transition.

Contribution

The paper experimentally measures the elastocaloric effect in TmVO$_4$, revealing its large strain-tunable entropy change and implications for cryogenic cooling technologies.

Findings

Large elastocaloric coefficient observed in TmVO$_4$

Entropy can be tuned by external strain near phase transition

Potential for efficient cryogenic cooling applications

Abstract

Adiabatic decompression of para-quadrupolar materials has significant potential as a cryogenic cooling technology. We focus on TmVO$_4$, an archetypal material that undergoes a continuous phase transition to a ferroquadrupole-ordered state at 2.15 K. Above the phase transition, each Tm ion contributes an entropy of $k_B \ln{2}$ due to the degeneracy of the crystal electric field groundstate. Owing to the large magnetoelastic coupling, which is a prerequisite for a material to undergo a phase transition via the cooperative Jahn-Teller effect, this level splitting, and hence the entropy, can be readily tuned by externally-induced strain. Using a dynamic technique in which the strain is rapidly oscillated, we measure the adiabatic elastocaloric coefficient of single-crystal TmVO$_4$, and thus experimentally obtain the entropy landscape as a function of strain and temperature. The measurement confirms the suitability of this class of materials for cryogenic cooling applications, and provides insight to the dynamic quadrupole strain susceptibility.