  We have studied the dependence of impurity vs. band effects in the appearance
of inverse giant magnetoresistance (IGMR) in Cu/Fe superlattices whit Cr.
Current in plane (CIP) and current perpendicular to the plane (CPP) geometries
are considered. For the calculation of the conductivities we have used the
linearized Boltzmann equation in the relaxation time approximation. Cr impurity
effects are taken into account through the spin dependent relaxation times and
the band effects through the semiclassical velocities obtained from the LDA
calculated electronic structure.
  The larger the Cr/Fe hybridization strength, the bigger is the tendency
towards
  IGMR. In particular, in CIP geometry roughness at these interfaces increases
the IGMR range.
  The results are compared with experiments and we conclude that the
experimental GMR curves can only be explained if Cr bands are present.
