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

The influence of Al concentration on the ⁵⁷Fe- and ¹¹⁹Sn-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.% ¹¹⁹Sn, 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 H̄ and the average isomer shift Ī; the average hf field H̄ and the average number of Al atoms in the first two neighboring shells, N̄A. 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 ⁵⁷Fe and 1290 kOe/s electron for ¹¹⁹Sn. From the correlations between H̄ and N̄A the changes in spin or charge densities caused by one Al atom per unit cell η have been deduced. From the Fe-site results η=0.10 was found for the changes in both the itinerant and localized spin densities. From the Sn-site results η=0.09 for itinerant and η=0.04 for localized spin-density changes have been deduced.