A 5 e Mossbauer study of a new series of rare-earth iron nitrides: R 2 Fe 17 N 3- delta

57 Fe Mossbauer spectra have been obtained at room temperature and at 15 K for R 2 Fe 17 and R 2 Fe 1 7 N 3- delta ( delta approximately=0.4) with R identical to Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y. The easy direction of magnetization of the R 2 Fe 17 compounds can be identified by analysis of the hyperfine field and quadrupole interactions. For rare-earth elements with J>3, the sixth-order crystal-field parameter B 66 determines the easy magnetization direction in the basal plane. In the nitrides, the average hyperfine field at 15 K increases by approximately 13% above the value in the parent compounds, from about 31 to 35 T, and it is anisotropic, being greatest when the magnetization lies along the c-axis. There is also an increase in the isomer shift of 0.12(2) mm s -1 . Spin reorientation transitions occur in the nitrides of Er and Tm; only the samarium nitride has an easy c-axis at room temperature, but Sm, Er and Tm all have easy c-axis magnetic structures at 15 K.