Very large magnetoimpedance (MI) in FeNi/Au multilayer film systems

This paper investigates the magnetoimpedance (MI) effect in miniature NiFe/Au/NiFe multilayer film systems with layer thickness of 0.5 μm produced by RF sputtering. The magnetic films have a well-established transverse anisotropy, which was achieved by imposing a large magnetic field during the deposition and further annealing. The influence of insulating Al2O3 layers between the inner conductor and the magnetic layers on MI was also considered. The use of insulation is proving not to improve the MI behavior in thin film systems. The basic three layer film with in-plane size of 50 μm × 5000 μm shows the impedance change of more than 150% with the maximal sensitivity of 30%/Oe in the frequency range of 200–500 MHz. We believe this is the highest sensitivity reported for such miniature film systems.