Lattice specific heat for the RMIn$_5$ (R = Gd, La, Y, M = Co, Rh) compounds: non-magnetic contribution subtraction

TL;DR

This paper develops a theoretical method to accurately subtract lattice contributions from specific heat measurements of magnetic materials, using density functional theory to identify optimal non-magnetic analogs across temperature ranges.

Contribution

It introduces a computational approach to select the best non-magnetic analogs for specific heat subtraction, improving the accuracy of magnetic contribution analysis in rare-earth compounds.

Findings

YRhIn$_5$ closely matches GdCoIn$_5$ across all temperatures

LaCoIn$_5$ better approximates GdRhIn$_5$ due to mass and volume effects

Including anharmonic effects aligns theory with experimental specific heat data

Abstract

We analyze theoretically a common experimental process used to obtain the magnetic contribution to the specific heat of a given magnetic material. In the procedure, the specific heat of a non-magnetic analog is measured and used to subtract the non-magnetic contributions, which are generally dominated by the lattice degrees of freedom in a wide range of temperatures. We calculate the lattice contribution to the specific heat for the magnetic compounds GdMIn$_5$ (M = Co, Rh) and for the non-magnetic YMIn$_5$ and LaMIn$_5$ (M = Co, Rh), using density functional theory based methods. We find that the best non-magnetic analog for the subtraction depends on the magnetic material and on the range of temperatures. While the phonon specific heat contribution of YRhIn$_5$ is an excellent approximation to the one of GdCoIn$_5$ in the full temperature range, for GdRhIn$_5$ we find a better agreement with LaCoIn$_5$, in both cases, as a result of an optimum compensation effect between masses and volumes. We present measurements of the specific heat of the compounds GdMIn$_5$ (M = Co, Rh) up to room temperature where it surpasses the value expected from the Dulong-Petit law. We obtain a good agreement between theory and experiment when we include anharmonic effects in the calculations.