Changes of Structure and Magnetic Properties of $(Ni_{80}Fe_{20}//Au//Co//Au)_N$ Multilayers as a Function of Repetition Number N

The influence of repetition number N on magnetoresistance, magnetic reversal and structure of sputtered $(Ni_{80}Fe_{20}//Au//Co//Au)_N$ multilayers was investigated. The multilayers are characterized by in-plane $(Ni_{80}Fe_{20})$ and out-of-plane (Co) magnetic anisotropy of ferromagnetic layers and show considerable magnetoresistance effect (ΔR/R) of the giant magnetoresistance type. Increased N results in an enhancement of ΔR/R from about 0.5% for N=1 up to above 5% for N=15. This enhancement is caused by: diminishing the role of electron scattering at the surfaces, decreasing the effect of structural imperfection and the lack of the perpendicular anisotropy of Co layer in the first period. The interpretation is corroborated by low ΔR/R value observed for N=1 and an evolution of the ΔR(H)/R dependence with increasing N. The anisotropy field of Co layers also increases with N.