Self-consistent embedded-cluster model for magnetic impurities: Fe, Co, and Ni in β′ - N

Substitutional transition-metal impurities occupying either Ni or Al sites in the intermetallic compound β′-NiAl with CsCl structure have been treated by a self-consistent molecular-orbital method. The electronic energy levels and charge and spin densities of MX8 clusters representing a central atom and its nearest neighbors and MX8Y6 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 β′-NiAl are discussed in connection with experimental resistivity, Mössbauer isomer shift, and NMR data.