A structural, magnetic, and Mossbauer spectral study of Dy2Fe17 and its hydrides

The structural and magnetic properties of the Dy2Fe17Hx compounds, where x is 0, 1, 2, 3, and 3.8, have been investigated by means of powder x-ray dif fraction, thermomagnetic and ac magnetic susceptibility measurements, and i ron-57 Mossbauer spectroscopy. The Dy2Fe17Hx compounds crystallize in a hex agonal Th2Ni17 -like structure which has both an iron-rich stoichiometry an d disorder of the Dy and Fe-Fe dumbbell sites. The increase in the lattice parameters, the magnetic ordering temperature, the saturation magnetization , and the dependence of the Mossbauer hyperfine parameters upon hydrogen co ntent support a two-step filling by hydrogen of the interstitial sites with hydrogen first filling the octahedral 6h sites for x < 3 and then partiall y filling the tetrahedral 12i sites for x=3 and 3.8. Neither the Mossbauer spectra nor the ac magnetic susceptibility measurements reveal any spin reo rientation in any of the compounds. The extent of the excess iron and the d isorder observed in all the compounds is confirmed by the Mossbauer spectra and the hyperfine parameters of the iron 4e sites are reported herein for the first time. Finally, the Mossbauer spectra indicate that the interstiti al hydrogen atoms partially occupying the tetrahedral 12i sites are jumping between these sites on the Mossbauer time scale. (C) 2000 American Institu te of Physics. [S0021-8979(00)06817-1].