Mossbauer spectral study of the magnetic properties of Ce2Fe17Hx (x=0, 1, 2, 3, 4, and 5)

The Mossbauer spectra of Ce2Fe17Hx, where x=0, 1, 2, 3, 4, and 5, have been measured and analyzed between 4.2 and 295 K. Because Ce2Fe17 exhibits a he lical magnetic order between 225 and 90 K and a fan magnetic order below 90 K, its Mossbauer spectra were fit with a distribution of hyperfine fields and theta angles for four of the eight magnetically inequivalent sites. Bec ause the hydrides exhibit a magnetization within the basal plane of the hex agonal cell, their Mossbauer spectra were fit with seven sextets. The four isomer shifts correlate with the Wigner-Seitz cell volume, the hyperfine fi elds correlate with the number of iron near neighbors and give estimates of the individual iron magnetic moments ranging from 0.91 mu (B) to 2.13 mu ( B), and the quadrupole splittings are in agreement with a point charge calc ulation. The temperature dependence of the hyperfine fields in Ce2Fe17 is i nsensitive to the transition from the fan to the helical magnetic structure , a transition which does not modify to any extent the iron electronic stru cture. As a result of the sudden ferromagnetic ordering which results from the presence of as little as one hydrogen per formula unit, the increase of 70 kOe in the weighted average hyperfine field upon hydrogenation is the l argest between x=0 and 1. The temperature dependence of the weighted averag e hyperfine field in the hydrides shows Brillouin behavior, a behavior whic h is slightly different for Ce2Fe17. The temperature dependence of the isom er shift yields a Debye temperature of 345 K. The variation of the hyperfin e parameters upon hydrogenation confirms that first the 9e octahedral site is filled by hydrogen, and second the 18g tetrahedral hydrogen site is fill ed.