ANOMALOUS THERMAL EXPANSION OF Sm,Fe,,Si, 8 .q

Crystallographic and magnetic properties of SmlFe17,Si, with x=O, 05,1.0,1.5,2.0, and 2.5 have been investi- gated. X-ray diffraction and thermomagnetic analyses showed that all samples studied are single phase with Th,Zn, structure. The Curie temperature increases with increasing Si content al- though the lattice parameters decrease. Anomalous thermal ex- pansion of Sm,Fe,,S$ was observed below Curie temperature by high temperature x-ray difPraction experiments. I. INTROUCTION The &Fel7 compounds crystallize in two closely related structure types: hexagonal ThzNi7 structure and rhombohedral Th?n17 structure. There are four crystallographically inequivalent Fe sites in these structures. The low Curie temperature of these compounds is usually attributed to the small Fe-Fe nearest- neighbour distance at the dumbbell site and the concomitant antiferromagnetic exchange interaction between correspond- ing Fe atoms in the structure.The negative exchange interaction also results in an anomalous thermal expansion of these compounds below Curie temperature( 11. The substitution of Si