Deviations from one-electron behavior in the Ag and Pd $M_{4,5}-\mathrm{VV}$ Auger spectra of ${\mathrm{Ag}}_c{\mathrm{Pd}}_{1-c}$ alloys

A systematic investigation of the Ag and Pd $M_{4,5}-\mathrm{VV}$ Auger spectra in the pure metals and in the ${\mathrm{Ag}}_c{\mathrm{Pd}}_{1-c}(0.1\mathrm{}<~c<~0.9)$ alloys is presented. The shape of the Auger spectra is discussed in relation to the values of the effective Coulomb interaction $U_{\mathrm{eff}}$ between the two holes present in the final state of the Auger transition and of the width $W$ of the one-electron local densities of states as obtained from $L{\beta }_{2,15}$ soft-x-ray emission bands. The Auger spectra of Ag in the metal and the alloys have a pronounced quasiatomic character, as can be expected from the $\frac{U_{\mathrm{eff}}}{2W}$ ratio which is found to be close to unity. The Auger spectrum of pure Pd ($\frac{U_{\mathrm{eff}}}{2W}\approx 0.4$) can be explained in terms of an atomic model in which strong band effects are present. For alloys with low-Pd content where Pd forms an impurity state, it is shown that final states other than the localized [$4d^2$] two-hole state have to be invoked to explain the line shape.