NEUTRON-DIFFRACTION AND MOSSBAUER-EFFECT STUDY OF THE PREFERENTIAL SILICON SITE OCCUPATION AND MAGNETIC-STRUCTURE OF ND2FE14-XSIXB

A neutron-diffraction study of Nd2Fe14-xSixB has shown that silicon pr eferentially occupies the 4c site in the transition-metal sublattice i n Nd2Fe14B. Silicon also exhibits a moderate preference for the 8j1 si te, is almost excluded from the 16k2 site, and avoids the 16k1, 8j2, a nd 4e sites. The silicon site occupancy is correlated with a preferenc e for a silicon atom to have rare-earth atoms in its coordination envi ronment. The Mossbauer spectra of Nd2Fe14-xSixB have been fit with a m odel which takes into account the distribution of near-neighbor enviro nments of an iron atom due to the presence of silicon. These fits show that the substitution of silicon in the near-neighbor environment of an iron atom primarily influences the long-range contributions to the hyperfine field experienced by the iron. The mechanism for the increas e in the Curie temperature when silicon is added to Nd2Fe14B-type magn ets is more subtle than previously believed, but can be explained by t he relative decrease in the proportion of short iron-iron bonds when s ilicon is substituted for iron.