Note on RKKY interactions in nearly-free electron systems

The RKKY interaction between localized magnetic moments via polarization of conduction electrons is calculated for systems with spherical, but non-quadratic conduction electron dispersion. It is shown that even rather small changes in the electron dispersion may produce large modifications of the density of electronic states and therefore deviations from the common RKKY expression derived for free electrons. The results might be important for the discussion of interaction mechanisms in amorphous ferromagnetic materials.