AN ANALYSIS OF IRON-IRON INTERATOMIC DISTANCES IN SEVERAL RARE-EARTH TRANSITION-METAL INTERMETALLICS

As a part of a systematic study of the dependence of iron-iron exchang e interactions on near neighbor iron-iron distances in rare earth tran sition metal magnetic materials, we have conducted a statistical analy sis of interatomic distances in Nd2Fe17, Nd2Fe14N3, and Nd2Fe17B. Resu lts, in general, support the notion that larger near neighbor iron-iro n distances promote higher Curie temperatures. In this work, special a ttention has been paid to the expansion of the Nd2Fe17 lattice due to interstitial nitrogenation and the accompanying increase in the Curie temperature. Within the unit cell, the expansion of the Nd2Fe17 lattic e due to nitrogenation is highly nonuniform. When nitrided, the distan ce between near neighbor 6c iron sites in Nd2Fe17 increases only sligh tly, by 0.021 Angstrom. However, the distances between other near neig hbor iron pairs separated by less than 2.45 Angstrom increases by abou t 0.04 Angstrom. The nitrogenation of Nd2Fe17 effectively reduces the number of near neighbor iron pairs separated by less than 2.45 Angstro m by 92%. However, near neighbor interatomic distances involving the 1 8h sites are the most affected by nitrogenation. Consequently, the 18h site may play a major role in the enhancement of the Curie temperatur e due to nitrogenation. (C) 1997 American Institute of Physics.