Magnetic properties of a new family of ternary rare-earth iron nitrides R2Fe17N3−δ (invited)

Abstract

A series of interstitial ternary nitrides R₂Fe₁₇N_3−δ 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 Sm₂Fe₁₇N_3−δ, 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 ≊ 1.0 MJ/m³ at 4.2 K for Y₂(Fe_1−xCo_x)₁₇N_3−δ when x≥0.2).