Structural, magnetic, and Mössbauer spectral study ofEr2Fe17and its hydrides

Abstract

The structural and magnetic properties of the ${\mathrm{Er}}_{2}{\mathrm{Fe}}_{17}{\mathrm{H}}_{x}$ compounds, where x is 0, 1, 2, 3, and 3.8, have been investigated by means of powder x-ray diffraction, thermal and ac magnetic susceptibility measurements, and iron-57 M\ossbauer spectroscopy. The ${\mathrm{Er}}_{2}{\mathrm{Fe}}_{17}{\mathrm{H}}_{x}$ compounds crystallize in the hexagonal ${P6}_{3}/\mathrm{mmc}$ space group with the ${\mathrm{Th}}_{2}{\mathrm{Ni}}_{17}$-like structure, a structure which has both an iron-rich stoichiometry and disorder of the erbium and iron--iron $4f--4f$ dumbbell sites. The increase in the lattice parameters, the magnetic ordering temperature, the saturation magnetization, and the dependence of the M\ossbauer spectral hyperfine parameters upon the hydrogen content reveal a two-step filling of the interstitial sites, with hydrogen first filling the octahedral $6h$ sites for $xl3$ and then partially filling the tetrahedral $12i$ sites for $x=3$ and 3.8. Neither the M\ossbauer spectra nor the ac magnetic susceptibility measurements reveal any spin reorientation in any of these compounds. In all of the compounds both the excess amount of iron and the expected disorder is confirmed by the M\ossbauer spectra and the hyperfine parameters of the iron $4e$ site are reported herein. Finally, the M\ossbauer spectra indicate that the interstitial hydrogen atoms partially occupying the tetrahedral $12i$ sites are jumping between these sites on the M\ossbauer time scale.