Self-consistent embedded-cluster model for magnetic impurities: Fe, Co, and Ni inβ′--NiAl

Substitutional transition-metal impurities occupying either Ni or Al sites in the intermetallic compound ${\ensuremath{\beta}}^{\ensuremath{'}}$-NiAl with CsCl structure have been treated by a self-consistent molecular-orbital method. The electronic energy levels and charge and spin densities of $M{X}_{8}$ clusters representing a central atom and its nearest neighbors and $M{X}_{8}{Y}_{6}$ clusters representing central, nearest-neighbor and second-nearest-neighbor atoms have been calculated in the Hartree-Fock-Slater spin-polarized model, using a numerical discrete variational method. Interaction of the impurity cluster with the crystal environment is represented by a pseudopotential derived from cluster calculations on the pure compound. Results for Fe, Ni, and Co impurities in ${\ensuremath{\beta}}^{\ensuremath{'}}$-NiAl are discussed in connection with experimental resistivity, M\"ossbauer isomer shift, and NMR data.