Thermal expansion of the magnetically ordering intermetallics RTMg (R = Eu, Gd and T = Ag, Au)

TL;DR

This study investigates the thermal expansion and magnetic phase transitions of Eu- and Gd-based intermetallics, revealing strong spin-phonon coupling and potential quantum phase transitions under moderate pressures.

Contribution

It provides new measurements of thermal expansion and pressure dependence in RTMg intermetallics with magnetic orderings, highlighting strong spin-phonon interactions and possible quantum critical points.

Findings

Sharp peaks in thermal expansion coefficient at magnetic transitions

Large pressure dependences suggest strong spin-phonon coupling

Potential quantum phase transitions at moderate pressures

Abstract

We report measurements of the thermal expansion for two Eu$^{+2}$- and two Gd$^{+3}$-based intermetallics which exhibit ferro- or antiferromagnetic phase transitions. These materials show sharp positive (EuAgMg and GdAuMg) and negative (EuAuMg and GdAgMg) peaks in the temperature dependence of the thermal expansion coefficient $\alpha$ which become smeared and/or displaced in an external magnetic field. Together with specific heat data we determine the initial pressure dependences of the transition temperatures at ambient pressure using the Ehrenfest or Clausius-Clapeyron relation. We find large pressure dependences indicating strong spin-phonon coupling, in particular for GdAgMg and EuAuMg where a quantum phase transition might be reached at moderate pressures of a few GPa.