Low-temperature thermal (specific heat, $C_P)$ and magnetic [ac susceptibility, ${\chi }_{\mathrm{ac}},$ and isothermal magnetization $M\left(B\right)\mathrm{}]$ measurements on Ce$T_y{X}_{4-y}$ ferromagnets (with $T=\mathrm{Ni}$, Cu, Pd, Ag, Au, and $X=\mathrm{Ga}$, Al, with $0.3<y<\mathrm{}0.7)$ are reported. With the exception of $T=\mathrm{Ni}$, all compounds with $X=\mathrm{Ga}$ show a typical second-order ferromagnetic transition. In the case of $T=\mathrm{Ni}$, magnetic correlations set in at $T\approx {3T}_C$ ${(T}_C$ being the Curie temperature) and the $C_P\mathrm{}\left(T\right)\mathrm{}$ and ${\chi }_{\mathrm{ac}}\mathrm{}\left(T\right)\mathrm{}$ maxima (at 3.3 and 4.2 K, respectively) do not coincide, while the $M\left(B\right)\mathrm{}$ curves reveal an antiferromagnetic character at lower temperatures. In these systems, the magnetic entropy of the ordered phase is larger than 85% of $R\ln 2$, in coincidence with the low values of the Sommerfeld coefficient $\gamma <~10$ mJ/mol K${}^2$. For $T=\mathrm{Ag}$ and $X=\mathrm{Al}$, a strong diamagnetic signal was observed at $T_s=0.63\mathrm{}$ K in ${\chi }_{\mathrm{ac}}\mathrm{}\left(T\right)\mathrm{}$, with the characteristics of a superconducting component. The thermodynamical properties of these compounds confirm the lack of hybridization when the Ce atom is in a ferromagnetic ground state.

• Received 9 January 1997

DOI:https://doi.org/10.1103/PhysRevB.56.5380