MAGNETISM AND STRUCTURAL CHEMISTRY OF TERNARY GALLIDES LANIXGA4-X, CENIXGA4-X, PRNIXGA4-X, NDNIXGA4-X, SMNIXGA4-X, GDNIXGA4-X, TBNIXGA4-X AND LACO0.5GA3.5

Ternary gallides with the chemical formula (La, Ce, Pr, Nd, Sm, Gd, Tb) NixGa4 - x, (Ce, Pr, Nd, Sm)NiGa3 and LaCo0.5Ga3.5 have been synthesized from the elements by arc melting. From X-ray powder diffraction analysis the RENixGa4-x compounds and LaCo0.5Ga3.5 were found to be isostructural and to adopt the BaAl4-type structure. The homogeneous range at 600 °C for the CeNixGa4 - x phase has been established revealing a remarkable positive deviation from Vegard's rule. The existence of new ternary compounds RENiGa3 with the CePtGa3 type was observed for RE ; Ce, Pr, Nd, and Sm at the stoichiometric composition which, however, is found within the region of the BaAl4-type structure. Magnetic susceptibilities were determined over a temperature range from 2 to 900 K. Above LNT, magnetic behaviour of the rare earth compounds (except lanthanum and samarium) of both structural series is characterized by the paramagnetic contribution of the tripositive rare earth free-ion moments. LaNi0.75Ga3.25 and LaCo0.5Ga3.5 are weakly paramagnetic. Samarium-containing alloys are characterized by a typical Van Vleck-type paramagnetism of closely spaced multiplets. At very low temperatures (T<20 K) for the ceric-nickel-gallides ferromagnetism is encountered, whereas for (Sm, Gd, Tb)NixGa4 - x the coupling of the 4f moments is antiparallel. © 1990.