FARADAY ROTATION AND THE ELECTRONIC STRUCTURE OF ALLOYS.

The polar reflection Faraday effect (PRFE) can measure the variation in the shape of the Fermi surface of a class of noble metal based alloys. This class of alloys has a type of disorder that does not destroy the validity of the concepts of pure materials. The Fermi surface for this class of alloys can be defined and measured for all concentrations and its variation should qualitatively follow the rigid band model. PRFE measurements on AgAu, AgMg, and AgCd alloy systems have been performed. The changes in the AgAu alloy system Fermi surface are monotonic and small, permitting calculation by perturbation theory. The changes in the AgMg and AgCd Fermi surfaces are large, requiring calculation by the forward scattering approximation. In their alpha -phases, the variation of the Fermi surface with concentration is the same within experimental error, for AgMg and AgCd. The necks on the (111) Brillouin zone faces expand continuously and somewhat slower than the rigid band model as the concentration increases. No clear evidence is found for second touching within the alpha -phase in both alloys. The beta -phase Fermi surface of AgCd has appreciable necks which expand more rapidly with concentration increase than occurs in the alpha phase.