Mössbauer-effect study of spin- and charge-density changes in Fe-Al alloys

Abstract

The influence of Al concentration on the $^{57}\mathrm{Fe}$- and $^{119}\mathrm{Sn}$-site hyperfine (hf) fields and isomer shifts has been studied for a series of Fe-Al alloys containing up to 15 at.% Al and 0.8 at.% $^{119}\mathrm{Sn}$, with use of M\"ossbauer-effect spectroscopy. The observed changes of the hf fields and the isomer shifts have been interpreted in terms of spin- and charge-density changes, respectively. Linear correlations have been revealed between the following quantities: the hf field $H(0, 0)$ and the isomer shift $I(0, 0)$ of undisturbed neighbor configurations; the average hf field $\overline{H}$ and the average isomer shift $\overline{I}$; the average hf field $\overline{H}$ and the average number of Al atoms in the first two neighboring shells, ${\overline{N}}_{A}$. From the first two correlations the following hf coupling constants have been determined: (a) the hf coupling constant for $s$-like itinerant electrons yielding 528 kOe/s electron and 3108 kOe/s electron for Fe and Sn atoms, respectively, and (b) the average hf coupling constant yielding 987 kOe/s electron for $^{57}\mathrm{Fe}$ and 1290 kOe/s electron for $^{119}\mathrm{Sn}$. From the correlations between $\overline{H}$ and ${\overline{N}}_{A}$ the changes in spin or charge densities caused by one Al atom per unit cell $\ensuremath{\eta}$ have been deduced. From the Fe-site results $\ensuremath{\eta}=0.10$ was found for the changes in both the itinerant and localized spin densities. From the Sn-site results $\ensuremath{\eta}=0.09$ for itinerant and $\ensuremath{\eta}=0.04$ for localized spin-density changes have been deduced.