A magnetic, neutron-diffraction, and Mössbauer spectral study of the Ce2Fe17−xSix solid solutions

Abstract

The magnetic properties of a series of Ce2Fe17−xSix solid solutions with x equal to 0.0, 0.23, 0.4, 0.6, 0.8, 1.02, 1.98, and 3.20 have been studied by magnetic measurements, neutron diffraction, and Mössbauer spectroscopy. An x-ray-diffraction study indicates that the compounds adopt the rhombohedral Th2Zn17-type structure. The substitution of silicon for iron in Ce2Fe17 leads to a contraction of the a axis by 0.2%, an expansion of the c axis by 0.2%, and a consequent reduction of the unit-cell volume by about 0.2% per substituted silicon. Magnetization studies indicate that the Curie temperature increases uniformly from 238 K for Ce2Fe17 to 455 K for Ce2Fe14Si2. Powder neutron-diffraction results, obtained at 295 K, indicate both that the silicon atoms preferentially occupy the 18h sites and that the iron moments increase with increasing silicon content, an increase which is related to the increase in Curie temperature. The Mössbauer spectra have been fit with a binomial distribution of the near-neighbor environments in terms of a maximum hyperfine field Hmax for an iron with zero silicon near neighbors, and a decremental field ΔH per silicon near neighbor. The compositional independence of both the weighted average maximum hyperfine field and of the decremental field indicates that the silicon acts as a magnetic hole, a hole which does not perturb the magnetic moments at the iron sites. The compositional dependence of the weighted average isomer shift is explained in terms of an interband mixing of the iron 4s and silicon 2p bands, due to the reduction of the iron 18h bond lengths. This interband mixing affects the charge but not the spin distribution at the iron sites.

A magnetic and Mössbauer spectral study of SmFe11Ti, LuFe11Ti, and their respective hydrides

“…A similar linear dependence of the hyperfine field on n has been successful in our earlier [28][29][30][31] analyses of the Mössbauer spectra of a variety of R 2 Fe 17−x M x solid solutions. This model, has led to the components and the fits shown in Figs.…”

Magnetic and Mössbauer spectral study of ErFe11Ti and ErFe11TiH

“…In order to both build in constraints into the model and reduce the number of adjustable parameters, we assume that the three hyperfine parameters for each crystallographically inequivalent iron site vary linearly with the number, n, of titanium near neighbors, as given by for one additional titanium near neighbor. A similar linear dependence of the hyperfine field on the number of substitutional near-neighbor atoms has been successfully used [33][34][35][36] in the analysis of the Mössbauer spectra of the R 2 Fe 17Ϫx M x solid solutions. Hence, above the spin-reorientation temperature, the Mössbauer spectra of ErFe 11 Ti and ErFe 11 TiH are fit with nine sextets, which involve 18 hyperfine parameters, one linewidth, and one total absorption area.…”

Magnetovolume anomalies in Ce2Fe17−xMnx

“…According to [7,8], the changes of the lattice parameter c due to the substitution of nonmagnetic elements (e.g., Al, Ga) for Fe seem to have a large influence on the magnetic properties of Ce 2 Fe 17 . In our case the substitution of Mn for Fe in Ce 2 Fe 17 leads not only to nonmonotonic changes of the lattice parameters but also to the appearance of Mn-Mn and Fe-Mn exchange interactions at different sites.…”