Race-earth iron nitrides are emerging as an important class of magnetic mat
erials, In certain rare-earth iron compounds, the insertion of small atoms
such as nitrogen and boron has resulted in significant changes in the magne
tic properties in the form of higher Curie temperatures, enhanced magnetic
moments, and stronger anisotropies. In an attempt to understand some of the
above, we have focused on two nitride phases of Fe, namely Fe4N (cubic) an
d Fe16N2 (tetragonal). For the Fe16N2 phase, the average Fe moment reported
by different experimental groups varies over a wide range of values, from
2.3 mu(B), to 3.5 mu(B). We will discuss some of the recent experiments and
examine some related theoretical questions with regard to Fe having such a
n unusually large moment in a metallic environment, Employing a Hubbard-Sto
ner-like model in addition to local-density results, it is shown that an un
usually large on-site Coulomb repulsion is necessary if one is to obtain a
moment as large as 3.5 mu(B).