A Mössbauer effect study of the interstitial hydrides and nitride of Nd2Fe17

The Mössbauer effect spectra of Nd₂Fe₁₇H₃, Nd₂Fe₁₇H₅, and Nd₂Fe₁₇N₃ have been measured at several temperatures between 85 and 295 K and fitted with a model which is similar to that used for the analysis of the Mössbauer effect spectra of Nd₂Fe₁₇ and Nd₂Fe₁₇N_2.6. The weighted average isomer shift increases in going from Nd₂Fe₁₇ to its hydrides and nitride, an increase which results mainly from the lattice expansion. The changes in the individual isomer shifts upon hydrogenation may be understood in terms of the expansion of the Wigner-Seitz cell volume and the presence of hydrogen or nitrogen near neighbors at a specific site. The 295 K weighted average hyperfine field increases from 157 kOe in Nd₂Fe₁₇ to 243 kOe in Nd₂Fe₁₇H₃, 280 kOe in Nd₂Fe₁₇H₅, and 318 kOe in Nd₂Fe₁₇N₃, a sequence determined by the Curie temperatures. In contrast, the weighted average hyperfine field at 85 K and the saturation magnetization at 5 K for Nd₂Fe₁₇H₃ are lower than those of Nd₂Fe₁₇, presumably because of thec-axis lattice contraction which occurs upon hydrogenation of this compound. The main difference between the effect of hydrogenation and nitrogenation resides in the substantial increase observed for the 9d and 18h hyperfine fields upon nitrogenation.