MAGNETIC AND NEUTRON-DIFFRACTION STUDIES OF R2FE17-XALXC (R = Y, PR, TB AND HO) INTERMETALLIC COMPOUNDS WITH TH2ZN17-TYPE CRYSTAL-STRUCTURE

The crystal structure, site occupancy and intrinsic magnetic propertie s of R2Fe17-xAlxC (R = Y, Pr, Tb and Ho; x = 0-4) compounds have been studied. Dilute Al substitution for Fe increases the T-c and decreases the M-s for all four compounds. For x = 2, T, of 501, 476, 529 and 50 1 K and M-s (measured at 5 K) of 141, 115.6, 40 and 38 emu/g were obta ined for R = Y, Pr, Tb, and Ho, respectively. From neutron diffraction , it was found unexpectedly that C atoms prefer both the 9e and 18g si tes for R = Pr and Tb, which is different from the case of 9e site pre ference for R = Y and Ho. As the rare earth element changes from light rare earth (R = Y and Pr) to heavy rare earth (R = Tb and Ho), the Al site occupation on 6c and 18f increases while that on the Ish site de creases. However, the 18h site still exhibits the highest Al occupancy for all samples. The T-c values obtained on Tb2Fe17-xAlxC and Ho2Fe17 -xAlxC are higher than those of Y2Fe17-xAlxC and Pr2Fe17-xAlxC suggest ing that T-c may be more strongly influenced by the R-Fe exchange inte raction rather than the Fe-Fe exchange interaction.