The magnetism of Sm3Ag4Sn4 and Gd3Ag4Sn4

ac susceptibility measurements are in good agreement with the antiferromagnetic transition of the Sm compound (T-N = 9.1 K), while two different transitions are observed in the thermal behaviour of x(ac) for Gd3Ag4Sn4 at 22 and 8.2 K. Isothermal magnetisation measurements at 5 K confirm the antiferromagnetic ground state of the compounds. In the paramagnetic region Gd3Ag4Sn4 follows the Curie-Weiss law (mu(eff,) = 7.77 mu(B) and theta(p) = -64 K), while the non-Curie-Weiss behaviour of the Sm phase is discussed in terms of partial occupation of the low-lying J = 7/2 excited state by the Sm3+ ions. The values of the ordering temperatures of the two compounds do not seem to follow the de Gennes scaling.