Magnetic Ordering in Dilute Solid Solutions of Iron in Gold. I

Magnetic ordering in Au-Fe solid solutions with Fe concentrations between 0.8 and 8.0 at.% has been studied using the M\"ossbauer effect. The relative internal field for all solute concentrations scales with the reduced temperature and agrees qualitatively with either the $\ensuremath{\alpha}$-Fe magnetization curve or a Brillouin curve with $S=1$. The value of the hyperfine field extrapolated to zero Fe concentration and 0\ifmmode^\circ\else\textdegree\fi{}K is (66\ifmmode\pm\else\textpm\fi{}3)% of its value in $\ensuremath{\alpha}$ Fe. The resonance lines in the magnetic hyperfine spectra are broader than the paramagnetic-resonance lines, possibly because of an intrinsic width of the hyperfine field (\ensuremath{\approx} 10%), or relaxation effects. The magnetic transition temperature varies approximately as the square root of the Fe concentration. A positive quadrupole coupling is observed for Fe concentrations of 6.7 and 7.4 at.%, but is not detectable in the more dilute alloys. The isomer shift is essentially independent of Fe concentration. Temperature hysteresis is observed near the ordering temperature for an Fe concentration of 6.7 at.%, but it is not detectable for an Fe concentration of 1.7 at.%.