Magnetic and transport properties of NiFe/Ag and Co/NiFe/Co/Ag multilayers

We present a comprehensive study of the structural, magnetic, and transport properties of NiFe/Ag multilayers grown by magnetron sputtering onto substrates maintained at liquid-nitrogen temperature. The influence of the Ag thickness (${\mathit{t}}_{\mathrm{Ag}}$), NiFe thickness (${\mathit{t}}_{\mathrm{NiFe}}$), and number of bilayers (n) has been studied. These multilayers exhibit antiferromagnetic and biquadratic coupling for 9 Å<${\mathrm{t}}_{\mathrm{Ag}}$<12.5 Å. For a given Ag thickness in this interval, the saturation field is inversely proportional to ${\mathit{t}}_{\mathrm{NiFe}}$. Furthermore, giant magnetoresistance (GMR) is observed with a maximum amplitude for ${\mathit{t}}_{\mathrm{NiFe}}$≊25 Å. However, the maximum GMR sensitivity ΔR/R/H is obtained at larger NiFe thicknesses. The dependence of the resistivity and magnetoresistance on the thickness of the NiFe layers has been analyzed within the Camley and Barnas semiclassical theory. The effect of adding thin layers of Co at the NiFe/Ag interfaces has also been investigated. A doubling of the GMR amplitude at room temperature and a significant increase in the saturation field are observed with the introduction of only one atomic plane of Co at each NiFe/Ag interface. A quantitative analysis of the data shows that the increase of the GMR is due to a better transmission of the spin-up electrons through the NiFe/Co/Ag interface than through the NiFe/Ag interface. The results are interpreted in terms of a reinforcement of the magnetic ordering at the NiFe/Co/Ag interfaces, and correlatively a reduction of the interfacial magnetic scattering caused by the presence of the Co layer. © 1996 The American Physical Society.