# Retrieving CeB$_6$'s lost magnetic entropy

## TL;DR

This study clarifies the magnetic entropy behavior of CeB6, showing it aligns with a quadruplet ground state above 30 K, but exhibits anomalies at lower temperatures due to cage effects and crystal field splitting.

## Contribution

The paper provides new specific heat measurements and an improved model for phonons and crystal fields in CeB6, resolving previous inconsistencies in magnetic entropy data.

## Key findings

- Magnetic entropy plateau observed above 30 K consistent with quadruplet ground state.
- First-order antiferromagnetic transition characterized with latent heat.
- Anomalous entropy reduction below 30 K linked to crystal field splitting by rare-earth movement.

## Abstract

The reported temperature variations of CeB6 s magnetic entropy are inconsistent with the fourfold degeneracy of the crystal field ground state. This old question is here addressed through new specific heat measurements and an improved description, in the cage context, of both the phonons and crystal field contributions to the specific heat. The antiferromagnetic transition is characterized as first-order and its latent heat determined. From the phonons dispersion for a cage compound, the lattice specific heat contribution is derived from the LaB6 data. Once corrected for the first-order transition and lattice contributions, the magnetic entropy displays the characteristic plateau of the quadruplet crystal field ground state, but at temperatures in excess of 30 K. Below 30 K, as the ordering temperature is approached, the magnetic entropy is substantially reduced. This anomalous temperature dependence is consistent with a crystal field ground state split by the rare-earth movement, a phenomenon specific to rare-earth cage compounds.