Ruderman-Kittel-Kasuya-Yosida interactions between spin distributions of arbitrary shape

The net Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between well-separ ated spin distributions can be mapped onto a RKKY interaction between two p oint-like effective moments. The effective moments, which a strongly oscill ating dependence on the size, shape, and orientation of the spin distributi on, are discussed for a variety of microscopic and macroscopic configuratio ns. Particular emphasis is on the relation between RKKY interactions and ba nd-structure Heisenberg exchange constants in itinerant magnets and on two- ion anisotropy contributions to the magnetocrystalline anisotropy of rare-e arth ions. (C) 2000 American Institute of Physics. [S0021-8979(00)50608-2].