Stiffness-constant variation in nickel-based alloys: Experiment and theory

Recent measurements of the spin-wave stiffness constant in several nickel alloys at various concentrations are interpreted within a random-phase approximation, coherent-potential approximation (RPA-CPA) band model which uses the Hartree-Fock approximation to treat the intraatomic correlations. We give a theoretical description of the possible impurity states in the Hartree-Fock approximation. This allows the determination of the Hartree-Fock solutions which can account for the stiffness-constant behavior and the magnetic moment on the impurity for all the investigated alloys. For alloys such as $\mathrm{Ni}\mathrm{Cr}$, $\mathrm{Ni}\mathrm{V}$, $\mathrm{Ni}\mathrm{Mo}$, and $\mathrm{Ni}\mathrm{Ru}$ the magnetizations of which deviate from the Slater-Pauling curve, our determination does not correspond to previous works and is consequently discussed. The limits of the model appear mainly due to local-environment effects; in the case of $\mathrm{Ni}\mathrm{Mn}$, it is found that a ternary-alloy model with some Mn atoms in the antiferromagnetic state can account for both stiffness-constant and magnetization behaviors.