An [formula omitted] Mössbauer spectral study of Gd 2Fe 17H x (for x=0, 3, and 5) and Sm 2Fe 17D 5

Abstract

The Mössbauer spectra of Gd 2Fe 17H x (for x=0, 3, and 5) and Sm 2Fe 17D 5 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 enviornment of the four crystallographically inequivalent iron sites, and the structural changes occuring 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 R 2Fe 17, to R 2Fe 17H 3, to R 2Fe 17H 5, and finally to R 2Fe 17N 3, 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 R 2Fe 17 and R 2Fe 17H 3 is at a maximum for the gadolinium compounds in agreement with their higher Curie temperatures. Pr 2Fe 17H 3 and Sm 2Fe 17N 3, which both exhibit axial magnetization, show large 85 K weighted average hyperfine fields than the remaining R 2Fe 17H 3 and R 2Fe 17N 3 compounds, respectively. Finally, the differences in the 18h iron site environment, due to the insertion of the fourth and fifth hydrogen atoms into R 2Fe 17H 5, where R is Nd, Sm, and Gd, are not observed in the Mössbauer spectra, and hence the hydrogen atoms on the 18g tetrahedral interstitial sites must be rapidly moving on the Mössbauer timescale. The magnetization curves of Sm 2Fe 17 and Sm 2Fe 17D 5 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.