Abstract
The effects of four different kinds of impurity δ-layer inserted into the Co layer of Co/Cu multilayers were investigated. Two completely different behaviours were found. Very small fractions of a monolayer of Ta or Cr increased the remanence of our multilayers up to almost 100%, destroying completely the giant magnetoresistance (GMR). This does not happen when an even larger amount of Cu or Pd is embedded in the Co layer, good antiferromagnetic coupling is maintained. In this case the remanence of the structure only increases by 20% for roughly an order of magnitude higher quantity of material, and naturally this still gives good values of the GMR. The decrease of the GMR is entirely explained in terms of a loss of antiferromagnetic alignment due to weaker indirect exchange coupling over the Cu spacer—even though this spacer layer remains pure Cu. These effects have been explained in terms of the magnetic properties of the different elements used as impurity affecting the spin-dependent reflectivity for electrons of the Co/Cu interfaces.