The exchange coupling and spin waves in metallic magnets: removal of the long-wave approximation

A well-known connection between the magnetic susceptibility and the effective exchange parameter is analyzed. It is shown that all current computational schemes use a long-wave approximation which is suitable only for localized moments systems. A corresponding smallness parameter is derived in real and reciprocal space. General 'inverse susceptibility' approach is combined with a multiple scattering theory and applied for the studies of elementary metals Fe, Ni and Gd. It is shown how the proposed approach significantly improves the description of the exchange coupling between nearest atoms, the spin wave spectrum at large wave vectors for the itinerant degrees of freedom in metallic magnets. A consistent usage of this method leads to the proper description of magnetic short-range order effects. (C) 2003 Elsevier Science B.V. All rights reserved.