⁵⁷Fe Mössbauer Spectral Study of Gd₂Fe₁₇Hₓ (for x = 0, 3, and 5) and Gd₂Fe₁₇Hₓ

The Mossbauer spectra of Gd2Fe17Hx (for x = 0, 3, and 5) and Sm2Fe17D5 have been measured between 85 and 295 K and have been analysed with a model which takes into account the basal orientation of the iron magnetic moments, the near-neighbor environment of the four crystallographically inequivalent iron sites, and the structural changes occurring upon hydrogen or deuterium insertion. The temperature dependences of the individual iron site isomer shifts and hyperfine fields follow the expected second-order Doppler shift and Brillouin law behavior, respectively, and provide support for the adequacy of the fitting model. The increases in the isomer shifts upon going from R2Fe17, to R2Fe17H3, to R2Fe17H5, and finally to R2Fe17N3, where R is a rare-earth atom, correlate well with the observed increases in the unit-cell volume and the iron Wigner-Seitz cell volumes upon hydrogen and nitrogen insertion. The 85 K weighted average hyperfine field in R2Fe17 and R2Fe17H3 is at a maximum for the gadolinium compounds in agreement with their higher Curie temperatures. Pr2Fe17H3 and Sm2Fe17N3, which both exhibit axial magnetization, show large 85 K weighted average hyperfine fields than the remaining R2Fe17H3 and R2Fe17N3 compounds, respectively. Finally, the differences in the 18h iron site environment, due to the insertion of the fourth and fifth hydrogen atoms into R2Fe17H5, where R is Nd, Sm, and Gd, are not observed in the Mossbauer spectra, and hence the hydrogen atoms on the 18g tetrahedral interstitial sites must be rapidly moving on the Mossbauer timescale. The magnetization curves of Sm2Fe17 and Sm2Fe17D5 have been measured at 5 and 300 K. The increase in the saturation magnetization upon deuterium insertion is well explained by the increase in the Curie temperature and correlates very well with the increase in the 85 K weighted average hyperfine field