Structural and magnetic properties of rare earth iron nitride series R₂(Fe_1−xCo_x)₁₇N_3−δ

The structural and magnetic properties of ternary nitride compounds R₂(Fe_1−xCo_x)₁₇N_3−δ with R=Ce, Pr, and Nd have been studied. X‐ray diffraction results show that nitrides are formed in a limited range of x in each series and the rhombohedral Th₂Zn₁₇ structure of their parent compounds is retained with an expansion in the unit cell volume. The room temperature saturation magnetization of nitrides is greater than that of the parent compounds for low Co concentrations. The 3d sublattice anisotropy is modified upon nitrogenation. All of the terminal compounds R₂Fe₁₇N_3−δ have their easy direction of magnetization in the basal plane. However, easy direction of magnetization shifts from planar to axial for x≊0.5 in the R₂(Fe_1−xCo_x)₁₇ series with R=Ce and Pr. This planar to axial transition of easy direction of magnetization shifts towards lower x (x≊0.15) in the nitride series R₂(Fe_1−xCo_x)₁₇N_3−δ for R=Ce, and is not observed for R=Pr and Nd. The results are interpreted in terms of enhancements in competing 3d sublattice (axial) and R sublattice (planar) anisotropies on nitrogenation, with Ce being essentially in the nonmagnetic intermediate valence state.