The magnetism of Sm 3Ag 4Sn 4 and Gd 3Ag 4Sn 4

Abstract

The magnetic properties of the ternary intermetallic compounds Sm 3Ag 4Sn 4 and Gd 3Ag 4Sn 4 are presented. Both phases crystallise in the orthorhombic oI22-Gd 6Cu 8Ge 8 type structure, space group Immm, and, from dc magnetisation measurements, display antiferromagnetic ordering at low temperatures: T N = 9 K for Sm 3Ag 4Sn 4 and 8 K for Gd 3Ag 4Sn 4. 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 χ ac for Gd 3Ag 4Sn 4 at 22 and 8.2 K. Isothermal magnetisation measurements at 5 K confirm the antiferromagnetic ground state of the compounds. In the paramagnetic region Gd 3Ag 4Sn 4 follows the Curie–Weiss law ( μ eff. = 7.77 μ B and θ 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 Sm 3+ ions. The values of the ordering temperatures of the two compounds do not seem to follow the de Gennes scaling.