Giant magnetoresistance of copper/permalloy multilayers

Current perpendicular (CPP) and current in-plane (CIP) magnetoresistances (MR) have been measured on sputtered Cu/Py (Py=Permalloy) multilayers at 4.2 K. The CPP-MR is several times larger than the CIP-MR. For fixed Py layer thickness, t(Py) = 1.5 nm, both the CPP and CIP MR's show oscillations with increasing tc, with a period similar to that previously reported for the CIP-MR. The CPP data for Cu thicknesses large enough that exchange interactions between Py layers are small are analyzed using the two spin-current model for both infinite and finite spin-diffusion length in Py. The very low coercive field of Py leads to a larger than usual uncertainty in the derived parameters, because of the uncertainty in the degree of antiparallel alignment required for the analysis. Three alternative analyses give bulk and interface spin-dependent anisotropy parameters, beta, and gamma, of comparable size, so that both must be considered in determining the CPP-MR. Our preferred values, based upon an assumed I-sf(Py) = 5.5 +/- 1 nm, are beta = 0.65 +/- 0.1 and gamma = 0.76 +/- 0.1. These values produce good fits to the CPP-MR's of Co/Cu/Py/Cu multilayers. [S0163-1829(98)01442-8].