COMPARATIVE-STUDY OF THERMAL AND MAGNETIC-PROPERTIES OF CETYX4-Y FERROMAGNETS

Low-temperature thermal (specific heat, C-P) and magnetic [ac suscepti bility, chi(ac), and isothermal magnetization M(B)] measurements on Ce TyX4-y ferromagnets (with T = Ni, Cu, Pd, Ag, Au, and X = Ga, Al, with 0.3 < y < 0.7) are reported. With the exception of T = Ni, all compou nds with X = Ga show a typical second-order ferromagnetic transition. In the case of T = Ni, magnetic correlations set in at T approximate t o 3T(C), (T-C being the Curie temperature) and the C-P(T) and chi(ac)( T) maxima (at 3.3 and 4.2 K, respectively) do not coincide, while the M(B) curves reveal an antiferromagnetic character at lower temperature s. In these systems, the magnetic entropy of the ordered phase is larg er than 85% of Rln2, in coincidence with the low values of the Sommerf eld coefficient gamma less than or equal to 10 mJ/mol K-2. For T = Ag and X = Al, a strong diamagnetic signal was observed at T-s = 0.63 K i n chi(ac)(T), 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.