Charging and the Magnetic Susceptibility of Silver-Gold and Alpha-Phase Copper-Gold Alloys

Abstract

Measurements are presented of the total mass magnetic susceptibility of Ag-Au alloys in the approximate range 6-300\ifmmode^\circ\else\textdegree\fi{}K, and $\ensuremath{\alpha}$-phase Cu-Au alloys at 292\ifmmode^\circ\else\textdegree\fi{}K. By making certain simplifying approximations, estimates of the values of the Pauli paramagnetic spin susceptibility of the free electrons in the pure metals and in the alloys have been made from these data. These values are then used to test a deduction from Stern's theory; namely, that as a result of charging, the variation of the fractional change in the density of electron states at the Fermi level from the linear interpolation between its values for the pure constituents can be expressed by $\mathrm{Kx}(1\ensuremath{-}x)$, where $x$ is the fractional amount of one of the constituents and $K$ is a constant. $K$ should be determinable either from values of the low temperature electronic specific heat or from values of the Pauli spin susceptibility. The magnetic data lead to values of $K=\ensuremath{-}0.32 \mathrm{and} \ensuremath{-}1.66$ for the Ag-Au and the Cu-Au systems, respectively. The former value is in fair agreement with the empirical value obtained for Ag-Au from recent low-temperature electronic-specific-heat data. Unfortunately, there are insufficient specific-heat data to allow a similar comparison to be made for the Cu-Au system. It is shown that such a comparison could be a crucial test for the choice between the different interpretations of the dependence upon solute concentration of the electronic specific heat in the Ag-Au system given by Haga and by Stern.