STRUCTURAL CHEMISTRY AND MAGNETIC-BEHAVIOR OF TERNARY GALLIDES REPTXGA4-X (RE=LA, CE, PR, ND, SM)

Two new series of ternary gallides with the chemical formulae (La, Ce, Pr, Nd, Sm)Pt//xGa//4// minus //x and (Ce, Pr, Nd)PtGa//3 have been synthesized from the elements by arc melting. From the results of X-ray powder diffraction analysis the REPt//xGa//4// minus //x series of compounds was found to be isotypic and to crystallize with the BaAl//4-type structure. The homogeneous range at 600 degree C of each of the REPt//xGa//4// minus //x phases was established revealing remarkable deviations from Vegard's rule. Magnetic susceptibilities were determined over a temperature range from 2 K to 1100 K. Above liquid nitrogen temperature, magnetism of the cerium, praseodymium and neodymium compounds of both structural series is characterized by the paramagnetism of the tripositive rare earth free-ion moments. LaPt//0//. //7//5Ga//3//. //2//5 is a very weak temperature-independent paramagnet. Samarium-containing alloys are typical Van Vleck-type paramagnets of closely spaced multiplets. At very low temperatures the onset of ferromagnetic ordering of the RE sublattice is encountered; the transition temperatures depend on the d metal concentration.