CRYSTALLOGRAPHIC DATA AND MAGNETIC-PROPERTIES OF NEW RTX COMPOUNDS (R-EQUIVALENT-TO-LA-SM, GD T-EQUIVALENT-TO-RU, OS X-EQUIVALENT-TO-SI, GE) - MAGNETIC-STRUCTURE OF NDRUSI

Investigations made by powder X-ray diffraction, susceptibility measur ements and neutron diffraction experiments on new ternary silicides RR uSi (R = La-Sm, Gd), germanides RRuGe (R = La-Sm) and CeOsSi are repor ted. All these new compounds crystallize in the well-known tetragonal structure of the CeFeSi type (space group P4/nmm). This structure, whi ch is closely related to the ThCr2Si2- and TbFeSi2-type structures, ca n be described as isolated ''ThCr2Si2 blocks'' (BaAl4 slab) connected via R-R contacts. LaRuSi and LaRuGe are Pauli paramagnets, while CeRuS i, CeRuGe and CeOsSi are Curie-Weiss paramagnets down to 4.2 K with ef fective moments of 2.56, 2.55 and 2.03 mu(B) respectively. GdRuSi and the Sm silicide and germanide behave ferromagnetically below 85, 65 an d 45 K respectively, whereas the Pr and Nd compounds are antiferromagn etic with Neel temperatures of about 74 K (Si) and about 64 K (Ge). Ne utron diffraction experiments show that NdRuSi has a collinear antifer romagnetic structure which consists of ferromagnetic (001) Nd layers ( with moments perpendicular to the layers) antiferromagnetically couple d along the c axis in the sequence + - - + (mu(Nd) = 2.81(5) mu(B)). T he results are discussed and compared with those obtained on the close ly related RRu2Si2 and isotypic RFeSi and RCoGe compounds.