An Fe-57 Mossbauer spectral study of Gd2Fe17Hx (for x=0, 3, and 5) and Sm2Fe17D5

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 whi ch takes into account the basal orientation of the iron magnetic moments, t he 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 adequ acy of the fitting model. The increases in the isomer shifts upon going fro m R2Fe17, to R2Fe17H3, to R2Fe17H5, and finally to R2Fe17N3, where R is a r are-earth atom, correlate well with the observed increases in the unit-cell volume and the iron Wigner-Seitz cell volumes upon hydrogen and nitrogen i nsertion. 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 magn etization, show large 85 K weighted average hyperfine fields than the remai ning R2Fe17H3 and R2Fe17N3 compounds, respectively. Finally, the difference s in the 18 h 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 obs erved in the Mossbauer spectra, and hence the hydrogen atoms on the 18 g te trahedral interstitial sites must be rapidly moving on the Mossbauer timesc ale. The magnetization curves of Sm2Fe17 and Sm2Fe17D5 have been measured a t 5 and 300 K. The increase in the saturation magnetization upon deuterium insertion is well explained by the increase in the Curie temperature and co rrelates very well with the increase in the 85 K weighted average hyperfine field. (C) 1999 Elsevier Science B.V. All rights reserved.