Origin of the missing low-temperature magnetic entropy in Yb2O2S

Determine whether the magnetic entropy missing from the measured low-temperature entropy release of Yb2O2S is released below the experimental temperature range or instead reflects a dynamic component of the state realized below its Néel temperature.

Background

The specific heat of Yb2O2S exhibits a sharp lambda anomaly near its antiferromagnetic ordering temperature, but integration of the magnetic specific heat yields only 4.06 J·mol⁻¹·K⁻¹, approximately two-thirds of the R ln(2) entropy expected for an effective spin-1/2 Kramers-doublet ground state. Because the measurements extend only down to 1.8 K, the authors identify two unresolved explanations for the missing entropy: additional entropy release at lower temperatures or dynamical behavior associated with the ordered state below the Néel temperature.

References

This value is significantly lower than the $R\ln{(2)}$ for a $S_{\text{eff}$~=~1/2 Kramers doublet ground state, corresponding to only two-thirds of the expected entropy release. This suggests that there may be additional entropy release below the measured temperature range or that there is a dynamic component to the state realized below $T_{\text{N}=3.0$~K.

— Rare-earth oxysulfides RE$_2$O$_2$S as model mixed-anion frustrated magnets  (2608.26023 - Ferrenti et al., 26 Aug 2026) in Section 2, subsection “Specific heat,” subsection “Yb2O2S”