Polar-reflection faraday effect and the Fermi surface of -phase silver-magnesium and silver-cadmium alloys

The Fermi surfaces of -phase disordered AgCd and AgMg alloys have been studied using the polar-reflection Faraday effect. Concentrations as high as 39.3-at.% Cd and 30.0-at.% Mg were obtained. It is shown that the uncertainty in the energy of states on the Fermi surface is small compared to changes which occur on alloying. Thus in both alloy systems, the Fermi surface is still a valid concept to use in discussing electronic properties of the concentrated alloys. It is found that the Fermi surfaces of both AgMg and AgCd change the same with concentration within experimental error up to 30 at.%, the maximum solubility of Mg in the phase. The Fermi-surface necks continually increase in size faster than the belly dimensions with increasing Cd and Mg content. There is some evidence that the AgCd Fermi surface may have a second contact near 40-at.% Cd. By comparison with room-temperature Hall-effect measurements, it is determined that for concentrated alloys the ratio of the room-temperature relaxation time on the belly, B,to that on the neck, N, is BN=10.2 for both AgMg and AgCd. In spite of the similarities of the Fermi surfaces for both AgMg and AgCd, only AgCd satisfies the Hume-Rothery rules. This is the first experimental evidence that the simple explanation that the Hume-Rothery rules depend only on Fermi-surface properties of the phase is inadequate.