Modified exchange interactions in dilute alloys

The Rudermann-Kittel interaction between spins centred on two impurity atoms in a crystal is examined by a Green function method. Since the impurity atoms have different spin-independent potentials the local charge density is changed and this modifies the R-K interaction. In general there is a change in amplitude and a phase change in the oscillations. Calculations have been made using the free electron model and the tight-binding model for a simple cubic lattice, assuming that the defects cause a change of potential which is short range. It is found that large enhancements of the interaction can occur if the defect gives a resonance close to the Fermi energy. Possible experiments whose interpretation is affected by these effects are discussed.