Mössbauer study of the hyperfine interaction of57FeinY1−sCo5+2sand related compounds

Abstract

The magnetic and electric hyperfine interaction and the relative fractions of dilute ${}^{57}\mathrm{Fe}$ nuclei on the four Co sites of ${\mathrm{Y}}_{1\ensuremath{-}s}{\mathrm{Co}}_{5+2s}$ have been investigated by M\ossbauer spectroscopy as a function of the relative number $s$ of Y atoms substituted by Co dumbbells. We also report M\ossbauer measurements of ${}^{57}\mathrm{Fe}$ in ${\mathrm{GdCo}}_{5},$ ${\mathrm{SmCo}}_{5},$ and ${\mathrm{Sm}}_{2}{\mathrm{Co}}_{17}(\mathrm{rh}).$ The $s$ dependence of the relative M\ossbauer fractions of ${}^{57}{\mathrm{F}\mathrm{e}:\mathrm{Y}}_{1\ensuremath{-}s}{\mathrm{Co}}_{5+2s},$ together with previous neutron diffraction results, allows an experimental site-hyperfine field assignment. The Fe atoms strongly favor the dumbbell sites at the expense of sites $6l$ of the hexagon surrounding the Co pair, while sites $2c$ and $3g$ are randomly occupied. In stoichiometric $R{\mathrm{Co}}_{5}$ ($R=\mathrm{Y},$ Sm, Gd) we observe a sizable dumbbell concentration, which is probably caused by the precipitation of ${R}_{2}{\mathrm{Co}}_{17}$ favored by the impurity nature of the M\ossbauer probe. With the increasing number of nearest Co neighbors, the magnetic hyperfine field passes from site $3g$ through a minimum at site $2c$ towards the maximum ${\mathrm{H}}_{\mathrm{hf}}=31.5\mathrm{}\mathrm{T}$ at the dumbbell site. The $4f$ contribution to the magnetic hyperfine field is small; the changes upon substitution of Y by $R=\mathrm{Gd},$ Sm are of the order of 10%.