Comparative study of magnetic, microwave properties and giant magnetoimpedance of FeNi-based multilayers with different structure

FeNi(100 nm)/Cu(500 nm)/FeNi(100 nm) and [FeNi(100 nm)/Cu(3 nm)]4/FeNi/Cu(500 nm)/[FeNi(100 nm)/Cu(3 nm)]4/FeNi(100 nm) multilayers in the shape of elongated stripes were prepared by rf-sputtering. Magnetization curves were measured by vibrating sample magnetometry. Magnetic domains were studied by the Bitter technique. Magnetoimpedance (MI) was studied as a function of the external magnetic field (H) for a frequency range of 1-300 MHz. Ferromagnetic resonance was measured as a function of the applied field for a 8.85 GHz frequency. Maximum MI sensitivities for total impedance at 75 MHz of 1.1 Ω/Oe (at 3.0 Oe) for [FeNi/Cu]4/FeNi/Cu/[FeNi/Cu]4/FeNi and 0.8 Ω/Oe (at 6 Oe) for FeNi/Cu/FeNi were obtained. Despite the increase of the magnetic inhomogeneities related to small contribution of mixed interfaces in the [FeNi/Cu]4/FeNi/Cu/[FeNi/Cu]4/FeNi structure, its MI response is more adequate for applications.