EFFECTS OF SI SUBSTITUTION ON THE MAGNETIC-PROPERTIES OF R(2)FE(17) COMPOUNDS WITH R=Y AND TM

X-Ray diffraction of R(2)Fe(17-x)Si(x) (R = Y and Tm) shows that the p repared samples are single phase, having the rhombohedral Th2Zn17-type structure and/or the hexagonal Th2Ni17-type structure. The substituti on of Si for Fe in R(2)Fe(17) (R = Y and Tm) leads to a strong increas e in the Curie temperature and a reduction in the unit cell volume. Th e Fe moments derived from Y2Fe17-xSix decrease with increasing Si conc entration from 2.0 mu(B) for x = 0 to 1.73 mu(B) for x = 3 as a result of magnetic dilution. The Tm moment is 6.0 +/- 0.3 mu(B), which is sl ightly lower than its free ion value. Samples of Tm2Fe17-xSix with x = 0-3 have a spin reorientation transition at low temperature. The spin reorientation temperature increases initially, then decreases with Si substitution, having a maximum value of 187.5 K at about x = 2.