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 exchange interactions on near neighbor iron-iron distances in rare earth transition metal magnetic materials, we have conducted a statistical analysis of interatomic distances in Nd2Fe17, Nd2Fe17N3, and Nd2Fe14B. Results, in general, support the notion that larger near neighbor iron-iron distances promote higher Curie temperatures. In this work, special attention 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 lattice due to nitrogenation is highly nonuniform. When nitrided, the distance between near neighbor 6c iron sites in Nd2Fe17 increases only slightly, by 0.021 Å. However, the distances between other near neighbor iron pairs separated by less than 2.45 Å increases by about 0.04 Å. The nitrogenation of Nd2Fe17 effectively reduces the number of near neighbor iron pain separated by less than 2.45 Å by 92%. However, near neighbor interatomic distances involving the 18h sites are the most affected by nitrogenation. Consequently, the 18h site may play a major role in the enhancement of the Curie temperature due to nitrogenation