Evidence for an ionic model of3dimpurities in metals

The orbital susceptibility of Co impurities in several metals is shown to be consistent with an ionic model suggested by Hirst which is generalized to include strong lifetime broadening of the many-body ionic energy levels by $k$-$d$ interaction. Kondo and both intra- and interconfiguration fluctuations are included. In CuCo and AuCo at low temperature the $3d$ ionic ground state is a $T_{1g}$ orbital triplet which is broadened to about 0.1 and 0.02 eV, respectively. In liquid CuCo the ionic state is apparently an unsplit ${}_{}{}^4{}_{}{}^{}F$ orbital. In nonmagnetic Co systems ionic linewidths may be several eV, but only a few distinct ionic orbitals are coupled into the ground state. In AlCo the ionic state is about 2.5 eV wide and is a superposition of either a ${}_{}{}^4{}_{}{}^{}F$ and ${}_{}{}^4{}_{}{}^{}P$ (intraconfiguration fluctuation), or a ${}_{}{}^4{}_{}{}^{}F$ and ${}_{}{}^5{}_{}{}^{}D$ (interconfigurational fluctuation). These considerations strongly indicate that localized spin fluctuation and other band-type models are not appropriate for $3d$ impurities.