Heat Capacity of Ferromagnetic Superconductors

Heat capacity measurements on two samples from each of the systems ${\mathrm{La}}_{1-x}{\mathrm{Gd}}_x$ and ${\mathrm{Y}}_{1-x}{\mathrm{Gd}}_x{\mathrm{Os}}_2$ show features which are correlated with the reported existence of both ferromagnetic and superconducting transitions. For one sample the measurements cover a wide enough temperature range to show that the entropy associated with the ordering of the gadolinium spins is the $\mathrm{xR}\ln 8$ expected for complete order. The heat capacities of the other samples are consistent with complete ordering. Superconducting transitions have been observed both above and below the maximum in the heat capacity associated with the spin ordering. The entropy differences between the normal and superconducting states show that superconductivity is not confined to small volume elements but probably extends throughout the sample.