  A quantum-mechanical description of the magnetic shape anisotropy, that is
usually ascribed to the classical magnetic dipole-dipole interaction, has been
developed. This is achieved by including the Breit-interaction, that can be
seen as an electronic current-current interaction in addition to the
conventional Coulomb interaction, within fully relativistic band structure
calculations. The major sources of the magnetic anisotropy, spin-orbit coupling
and the Breit-interaction, are treated coherently this way. This seems to be
especially important for layered systems for which often both sources
contribute with opposite sign to the magnetic anisotropy energy. Applications
to layered transition metal systems are presented to demonstrate the
implications of this new approach in treating the magnetic shape anisotropy.
