Magnetic Ordering in Dilute Solid Solutions of Iron in Gold. II. Electric Hyperfine Interactions

Abstract

The ${\mathrm{Fe}}^{57}$ M\"ossbauer spectra of Au-Fe alloys with Fe concentrations between 1.7 and 10.5 at.% at temperatures between the transition temperature and room temperature consist of a doublet superimposed on a central line which is an unresolved doublet. The centroids of the two doublets are separated by 0.06\ifmmode\pm\else\textpm\fi{}0.02 mm/sec. This is independent of Fe concentration and temperature. The outer doublet is associated with Fe ions with one or more Fe nearest neighbors, while the inner doublet is associated with Fe ions with no Fe nearest neighbors. The separation of the outer doublet lines is independent of Fe concentration and is 0.77\ifmmode\pm\else\textpm\fi{}0.02 mm/sec at 77\ifmmode^\circ\else\textdegree\fi{}K and 0.69\ifmmode\pm\else\textpm\fi{}0.02 mm/sec at 294\ifmmode^\circ\else\textdegree\fi{}K. The separation of the inner doublet is an order of magnitude smaller. It increases with increasing Fe concentration, but has no detectable dependence on temperature. These doublets are interpreted as quadrupole-split resonance lines. The electric field gradient (EFG) of the outer doublet probably arises from conduction electrons within the atomic sphere. The EFG of the inner doublet may arise from random strains, or Fe impurity charges beyond the nearest-neighbor shell, or both. An analysis of the temperature shifts gives an effective Debye temperature of (290\ifmmode\pm\else\textpm\fi{}40)\ifmmode^\circ\else\textdegree\fi{}K for Fe impurities in Au. The observed linewidths are independent of Fe concentration and temperature from 77 to 294\ifmmode^\circ\else\textdegree\fi{}K. The linewidths increase slightly at a few degrees above the transition temperature, perhaps because of the onset of magnetic-relaxation effects.