Giant magnetoresistance and antiferromagnetically coupled Co fraction in Co/Cu multilayers with varying number of periods

The giant magnetoresistive signal of Co/Cu multilayers as a function of the number N_Co of Co layers is experimentally investigated for Cu thicknesses of 1 nm, i.e. in the 1st antiferromagnetic maximum, and for Co layer thickness of 1 nm. The stacks were deposited by DC magnetron sputtering on an Fe buffer. The fraction F_AF of the film that couples antiferromagnetically is derived from the hysteresis curves. A correction of F_AF is required for the buffer and one Co layer. The F_AF of stack periods close to the buffer is about 1, while F_AF reduces at large stack thicknesses. The GMR of stacks with small thicknesses is limited by the diffuse scattering at the outer surfaces. The GMR of thicker stacks depends on F_AF and the resistivity. Furthermore, the meaning of F_AF is discussed. By optimizing N _Co, we achieved Δρ/ρ´s as high as 72% at room temperature