Magnetic and Mössbauer spectral study of ErFe11Ti and ErFe11TiH

Abstract

X-ray diffraction, isothermal magnetization at 5 and 300 K, ac magnetic susceptibility measurements between 5 and 200 K, and iron-57 Mössbauer spectral measurements between 4.2 and 295 K have been carried out on ErFe 11 Ti and ErFe 11 TiH. Hydrogen uptake has been measured by gravimetric analysis and the insertion of hydrogen into ErFe 11 Ti increases its magnetization, magnetic hyperfine fields, and isomer shifts as a result of the associated lattice expansion. Peaks and steplike changes in both the real and imaginary components of the ac magnetic susceptibility are observed at ϳ50 and 40 K for ErFe 11 Ti and ErFe 11 TiH, respectively, and are assigned to spin-reorientation transitions resulting from the temperature dependence of the sixth-order Stevens crystal-field term of erbium. The Mössbauer spectra have been analyzed with a model which considers both these spin reorientations and the distribution of titanium atoms in the near-neighbor environment of the three crystallographically distinct iron sites. The assignment and the temperature dependencies of the hyperfine fields and isomer shifts are in complete agreement with the WignerSeitz cell analysis of the three iron sites in ErFe 11 Ti and ErFe 11 TiH. The changes in the hyperfine field and isomer shift with the number of titanium near neighbors of the three iron sites are in agreement with the values observed for related titanium-iron intermetallic compounds.

A magnetic and Mössbauer spectral study of PrFe11Ti and PrFe11TiH

“…The average hyperfine field in PrFe 11 Ti increases upon hydrogenation, although the increase results only from increases of ∼0.5 T in the 8j and 8f hyperfine fields. This small increase in hyperfine field as compared to the increases observed in other RFe 11 TiH x compounds [11][12][13][14][15]19] may result from the small increase in unit-cell volume and consequently a small increase in the iron-iron near-neighbor distances.…”

“…Further, the model assumes a linear dependence of the hyperfine parameters upon the number of titanium nearest neighbors. The same model has been described in detail and successfully applied in the analysis of the Mössbauer spectra of several different RFe 11 TiH x compounds [11][12][13][14][15].…”

“…The assignment and temperature dependence of the three hyperfine fields for zero titanium near neighbor and their weighted average for PrFe 11 Ti and PrFe 11 TiH are shown in Fig. 4a and b, respectively.…”

“…For each site these sextets represent iron atoms with zero, one, and two or more titanium near neighbors, respectively. A further subdivision of these nine spectral components is necessary when the compound exhibits planar magnetic behavior [11,[13][14][15]. For PrFe 11 Ti and PrFe 11 TiH the best fit of the Mössbauer spectra is achieved when we assume that the magnetization lies along the [1 0 0] direction.…”

“…A further subdivision of these nine spectral components is necessary when the compound exhibits planar magnetic behavior [11,[13][14][15]. For PrFe 11 Ti and PrFe 11 TiH the best fit of the Mössbauer spectra is achieved when we assume that the magnetization lies along the [1 0 0] direction. In this case, because of the relative orientations of the hyperfine magnetic field and the principal axis of the electric field gradient, V zz , there is a further magnetic subdivision of the 8i and 8j sextets.…”