Screening of non-transition element impurities in iron

Publisher Website
Google Scholar
Abstract
A simple model is presented in which only the 4s electrons are considered to take part in the screening, the 3d electrons being assumed to be correlated and localised on the iron sites. The model is used to calculate the hyperfine field at the impurity nucleus and, assuming a positive polarisation of the 4s electrons and about one 4s electron per atom in the pure matrix, the impurity hyperfine field is found to cross from negative to positive values as the impurity potential becomes strong enough to form a bound state at the bottom of the band. Such a change in sign is observed experimentally between Al and Si in iron and recent measurements of the soft X-ray emission spectrum of an Fe 8 at% Al alloy confirm the presence of a resonant bound state on an Al impurity in iron. The covalent admixture between the impurity state and neighbouring 3d states is discussed.