Electronic structure of transition-metal impurities in copper

Abstract

The electronic structure of magnetic transition-metal impurities (Fe,Co,Ni) in Cu is calculated by means of a cluster approach and the local-spin-density approximation. The wave functions were expanded into Gaussians and no shape approximation to the potential was made. We report the results of the energy-level distribution in 13-atom fcc clusters of ${\mathrm{Cu}}_{13}$, ${\mathrm{Cu}}_{12}$Fe, and in 19-atom clusters (M${\mathrm{Cu}}_{12}$ ${\mathrm{Cu}}_6$, M=Cu,Fe,Co,Ni) which are in strong disagreement with Xα scattered-wave results. The local cluster density of states (DOS) agrees very well with the respective bulk and surface DOS of Cu metal. For the Fe impurity we obtain a local moment of 3.05${\mu }_B$, which is in good agreement with experiment and Green’s-function calculations. The spin densities show, besides the strong localized Fe moment, a negative polarization of the conduction electrons as indicated by a Mulliken population analysis or direct examination of the spin densities in the (100) plane. Previous observations of scattering in de Haas–van Alphen experiments, which showed that mainly spin-down states are involved, are in agreement with our local DOS. For the Co and Ni systems the impurity moment is reduced to 2.05${\mu }_B$ and 0.69${\mu }_B$; however, the Ni impurity might become nonmagnetic by including more Cu shells or proper boundaries in the calculation. This is indicated through the level distribution as well as the high correlation of magnetism in both Cu shells.