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, tPy=1.5 nm, both the CPP and CIP MR's show oscillations with increasing tCu 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, {β}, and {γ}, of comparable size, so that both must be considered in determining the CPP-MR. Our preferred values, based upon an assumed IsfPy=5.5±1 nm, are {β}=0.65±{}0.1 and {γ}=0.76±{}0.1. These values produce good fits to the CPP-MR's of Co/Cu/Py/Cu multilayers.