Calorimetric Evidence for a Singlet Ground State in Cu Cr and Cu Fe

Heat-capacity measurements show that the entropy reduction associated with the formation of the spin-compensated state in $\mathrm{Cu}\mathrm{Cr}$ is $R\mathrm{ln}(2S+1)$. The magnetic field dependence of the heat capacity of $\mathrm{Cu}\mathrm{Fe}$ suggests that at $T\ensuremath{\ll}{T}_{K}$ the susceptibility has the form $\ensuremath{\chi}={\ensuremath{\chi}}_{0}\ifmmode\times\else\texttimes\fi{}[1\ensuremath{-}15{(\frac{T}{{T}_{K}})}^{2}]$, which is consistent with the third law of thermodynamics.