MAGNETIC-PROPERTIES OF A NEW FAMILY OF TERNARY RARE-EARTH IRON NITRIDES R2FE17N3-DELTA

A series of interstitial ternary nitrides R2Fe17N3-delta has been prepared via a gas-solid reaction for R = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu, and Y. These nitrides have structures related to the Th2Zn17 or Th2Ni17 structures of the R2Fe17 parent compounds, but the unit cell volumes are 6%-7% greater, and the Curie temperatures are approximately 400 K higher. The Fe-Fe exchange interactions are increased by a factor of 2.8 by nitrogenation, whereas the R-Fe exchange interactions are little changed. All compounds exhibit easy-plane anisotropy at room temperature, except for Sm2Fe17N3-delta, which shows strong uniaxial anisotropy and may be used to make permanent magnets. The Er and Tm compounds exhibit spin reorientations below room temperature. The anisotropy due to the iron sublattices is easy plane (K1 = -1.3 MJ/m3 at 4.2 K for Y2Fe17N3), but it changes sign to easy axis with cobalt substitution (K1 almost-equal-to 1.0 MJ/m3 at 4.2 K for Y2(Fe(1-x)Co(x))17N3-delta when x greater-than-or-equal-to 0.2).