Optical absorption ofNiCualloys

A study of the optical absorption of $\mathrm{Ni}\mathrm{Cu}$ alloys for Cu concentrations from 2 to 13 at.% by a sensitive differential technique is presented. The experiment is analyzed for the difference in the optical conductivity between the alloy and pure Ni. The results are discussed in terms of the generalized Anderson model of dilute alloys. We also discuss the possible presence of $k$-non-conserving optical-absorption processes induced by the Cu impurities. The data appear to be consistent with the coherent-potential-approximation calculations of the density of states for $\mathrm{Ni}\mathrm{Cu}$ alloys. Edges at $\hslash \omega =0.9\mathrm{}$ eV and $\hslash \omega =1.7\mathrm{}$ eV are interpreted in terms of impurity density-of-states peaks 0.8 and 1.7 eV below $E_F$. The shape of the structure between 1.7 and 3 eV is consistent with an exchange splitting of about 0.6 eV in ferromagnetic Ni.