  Ab initio calculations for the giant magnetoresistance (GMR) in Co/Cu, Fe/Cr,
and Fe/Au multilayers are presented. The electronic structure of the
multilayers and the scattering potentials of point defects therein are
calculated self-consistently. Residual resistivities are obtained by solving
the quasi-classical Boltzmann equation including the electronic structure of
the layered system, the anisotropic scattering cross sections derived by a
Green's function method and the vertex corrections. Furthermore, the influence
of scattering centers at the interfaces and within the metallic layers is
incorporated by averaging the scattering cross sections of different impurities
at various sites. An excellent agreement of experimental and theoretical
results concerning the general trend of GMR in Co/Cu systems depending on the
type and the position of impurities is obtained. Due to the quantum confinement
in magnetic multilayers GMR can be tailored as a function of the impurity
position. In Co/Cu and Fe/Au systems impurities in the magnetic layer lead to
high GMR values, whereas in Fe/Cr systems defects at the interfaces are most
efficient to increase GMR.
