Magneto-impedance in sandwich film for magnetic sensor heads

This paper presents results on magneto-impedance (MI) in a NiFe/Co/NiFe sandwich film of 0.2 /spl mu/m thickness, which exhibits the impedance change up to 8% for a field of 4 Oe at a frequency of 400 MHz. The effect of voltage change with the field can be especially large (/spl sim/200% for 5 Oe) if the sandwich film is incorporated in a self oscillation circuit which can be directly used for magnetic sensor head applications. The comparative analysis of MI in a sandwich film and a single magnetic layer is given, demonstrating that the sandwich structure can show an increase in MI of about a factor of 6 over a single magnetic layer and the maximum MI effect occurs at frequencies of an order of magnitude lower.