SYNTHESIS, STRUCTURAL AND MAGNETIC-PROPERTIES OF THE INTERSTITIAL COMPOUNDS RCO9SI2CX WITH R = SM, ND, Y AND -LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1.8

The crystal structure and the magnetic properties of silicon substitut ed and carbon inserted R-Co based materials (R=Y, Nd, Sm) have been st udied. Carbon insertion in the RCo9Si2 compounds decreases the Curie t emperature and the magnetic moment mu(Co). In all the compounds, the a nisotropy of the cobalt sublattice is planar whereas the second order crystal electric field acting on R favours a uniaxial or a planar anis otropy for rare earth elements with positive (Sm) or negative (Nd) sig n of alpha(1) the second order Stevens' coefficient, respectively. Car bon insertion yields an increase of the 3d sublattice anisotropy, and probably of the R sublattice anisotropy. A comparison of the overall 3 d magnetic properties is made with some R-Fe intermetallics where p-el ements (C, N, Si) are alloyed. (C) 1998 Elsevier Science S.A. All righ ts reserved.