Magnetoresistance in rf-sputtered (NiFe/Cu/Co/Cu) spin-valve multilayers

A study of the variation of the magnetoresistance in (Ni80Fe20/Cu/Co/Cu) multilayers with the thicknesses tNiFe, tCo, and tCu of each type of component layer has been performed. The magnetoresistance (MR), which at 4.2 K is larger than 20% for many samples, has been measured for fields applied both parallel and perpendicular to the current. This allows a direct measurement of the anisotropic magnetorestistance as well as an estimate of the spin-valve contribution to the total MR. The dependence of the MR on tCu indicates the presence of an oscillatory interlayer exchange coupling through the Cu layers with a period of about 12 Å. The dependence of the MR on tNiFe and tCo was studied at tCu=50 Å, for which the coupling is negligible. In this limit, the variation of the MR is dominated by the thickness dependence of the NiFe and Co component layer coercivities, which determine the degree of antiparallel alignement obtained during magnetization reversal.