Magnetoresistance in (Co10 Å/Cu10 Å)_n multilayer films as n increases

Multilayers of Cu10 Å/(Co10 Å/Cu10 Å)n, where n is the number of bilayers, shows a nonlinear increase of magnetoresistance ratio (MR%) with increasing n. For each value of n the resistivity decreases with applied field. MR values at 4.2 K are less than 2% for n≤16 but increase to 38% at n=128. Conduction electron mean free paths (l), calculated from film resistivity as a function of total film thickness, increase from l=150 to 470 Å when the applied magnetic field changes from zero to 18 kOe. The values obtained for l indicate that for n≤16 MR is reduced by diffuse surface scattering while for n≥16 MR surface scattering is less important and the Co atomic moment ordering is the most important factor. About half the decrease in resistivity with field is associated with the final 2% increase in magnetization for fields above 5 kOe which we interpret in terms of Co interface disorder.