CRYSTAL-STRUCTURE AND MAGNETISM OF TERNARY COMPOUNDS RE(6)MSB(15), RE=LA, CE AND M=MN, CU, ZN

A series of novel ternary compounds RE(6)Msb(15) has been synthesized (a) via are melting elemental metal ingots (M = Mn or Cu) or (b) via r eaction sintering cold compacted powder blends (M = Zn). The crystal s tructure was solved for La6MnSb15 from single crystal X-ray counter da ta (La6MnSb15-type, Imm2, Z = 2, a = 1.5376, b = 1.9611, c = 0.4314 nm , R(F) = 0.067 for 923 reflections (\F-0\ > 3 sigma)). The Rietveld re finement of the crystal structure of Ce6MnSb15 using CuK alpha-X-ray d ata from a D5000 Siemens diffractometer confirmed atom order and cryst al symmetry Imm2 (R(I) = 0.049, R(F) = 0.031) and revealed small defic iencies in the Mn site as well as for one of the Sb sites. Employing X -ray powder Guinier techniques the new compounds were all found to be isostructural with the La6MnSb15 type. Magnetic measurements performed down to liquid helium temperature give evidence that both compounds C e6MnSb15 and Gd6ZnSb15 undergo an antiferromagnetic transition at 7 an d 15 K, respectively. Ce6ZnSb15 and Pr6ZnSb15 remain paramagnetic in t he temperature range investigated, whereas Sm6ZnSb15 is a Van-Vleck-ty pe paramagnet. (C) 1996 Academic Press, Inc.