The transition from bound to virtual 4f levels

Abstract

The ⁶³Cu and ²⁷Al solvent Knight shifts in CuAl and AgAl alloys, both with and without Gd impurities, have been measured across the two phase diagrams. In pure A1 the Gd impurities caused large Knight shifts which have previously been attributed to 4f levels lying in the conduction band, whereas Gd in pure Cu causes almost no core scattering. It is found that for both CuAl and AgAl solvents the core scattering becomes large rather abruptly at a solvent concentration of about 40 at. % Al. The transition from weak to strong core scattering of conduction states is interpreted as the transition of 4f core states from localized levels below the conduction band to virtual bound states lying in the conduction band. Other possible interpretations of the transition are also discussed.