A series of compounds with the ${\mathrm{ThMn}}_{12}$-type structure, R${\mathrm{Fe}}_{11.35}$${\mathrm{Nb}}_{0.65}$ (R=Y, Sm, Gd, Tb, Dy, Ho, Er, and Lu), were synthesized. The corresponding nitrides, obtained by gas-solid reactions, retained the same structure as their parent compounds, but with a relative volume expansion of 3%. The Nb atoms occupy the 8i sites in the ${\mathrm{ThMn}}_{12}$ structure. The highest Curie temperatures are 597 K and 773 K for ${\mathrm{GdFe}}_{11.35}$${\mathrm{Nb}}_{0.65}$ and its nitride, respectively. The average iron magnetic moment ${\mathrm{\mu }}_{\mathrm{Fe}}$ at T=1.5 K is 1.9${\mathrm{\mu }}_{\mathit{B}}$ for parent compounds and 2.1${\mathrm{\mu }}_{\mathit{B}}$ for the nitrides. By the introduction of nitrogen, the Fe-Fe exchange interaction is much strengthened while the R-Fe exchange interaction is slightly weakened. The enhancement of ${\mathrm{\mu }}_{\mathrm{Fe}}$ by the influence of interstitial nitrogen is about 11%. The Fe sublattices of R${\mathrm{Fe}}_{11.35}$${\mathrm{Nb}}_{0.65}$ compounds and their nitrides have an easy c-axis anisotropy. At T=1.5 K, the anisotropy constant ${\mathit{K}}_1$(Fe) is 25.7 K/f.u. for the parent compounds and 21.9 K/f.u. for the nitrides. The reduction of ${\mathit{K}}_1$(Fe) by the influence of interstitial nitrogen is about 17%. Spin-reorientation transitions were observed in ${\mathrm{DyFe}}_{11.35}$${\mathrm{Nb}}_{0.65}$ and ${\mathrm{ErFe}}_{11.35}$${\mathrm{Nb}}_{0.65}$ compounds. The complex magnetic behavior of R${\mathrm{Fe}}_{11.35}$${\mathrm{Nb}}_{0.65}$ at low temperatures can be explained by exchange and crystal-field-interaction models. The ${\mathrm{SmFe}}_{11.35}$${\mathrm{Nb}}_{0.65}$ compound has an anisotropy field of 10.0 T at room temperature. Its high Curie temperature and magnetization make it a potential candidate for applications as a permanent magnet.

• Received 27 September 1994

DOI:https://doi.org/10.1103/PhysRevB.51.2905