Polarized neutron reflectivity characterization of weakly coupled Co/Cu multilayers

Room temperature resistivity studies on (1 1 1) Co(6 nm)/Cu(6 nm) multilaye rs with weak interlayer coupling yield a giant magnetoresistance (GMR) of s everal percent for the as-prepared state relative to the saturated (i.e., l arge magnetic field) state. After application of a magnetic field, the magn etoresistance for the coercive state is only half to two-thirds as large. U sing specular and off-specular polarized neutron reflectivity, we have dete rmined the magnetic structure of these multilayers in the as-prepared and c oercive states. Measurements of as-prepared samples show a strong antiparal lel correlation of in-plane ferromagnetic Co domains across the Cu interlay ers. Ar the coercive held, the Co domains are uncorrelated along the growth direction. Thus, the larger GMR for the as-prepared state arises from long -range antiparallel magnetic order along the growth-axis direction that is destroyed upon application of a magnetic field. For both the as-prepared an d coercive states. the size of the in-plane ferromagnetic domains is approx imately 0.5-1.5 mu m. These domains give rise to pronounced diffuse scatter ing in rocking curves through the antiferromagnetic peak position. (C) 2000 Elsevier Science B.V. All rights reserved.