Mössbauer studies of interstitial rare earth-iron intermetallics

Two series of interstitial rare earth-iron intermetallics, R₂Fe₁₇N_3-σ and R₂Fe₁₇C_3-σ have been prepared by gas phase reaction from the R₂Fe₁₇ parent compounds (R=Ce, Pr, Nd, ... Lu and Y). The interstitials raise the Curie temperature of the compounds by 390 K in the case of N and 330 K in the case of C. Mössbauer spectra at 15 K and 293 K, and data as a function of temperature for R=Er and Tm are analysed to yield hyperfine interactions at the four sites, and information on the local magnetization and its orientation. The change in hyperfine field is not proportional to the change in magnetization produced by the interstitials, being much greater in the nitrides than the carbides. Likewise for the isomer shifts. These effects are discussed in terms of the differences in electronic structure of the nitrides and carbides.