Magnetic properties and magneto-impedance of cold-drawn permalloy-copper composite wires

The permalloy-copper composite wires consisting of high conductivity Cu inner core and NiFe outer shell were fabricated by a modified cold-drawn technique. The diameter of the Cu inner core was in 20-120 mu m range, and the NiFe outer shell was 10-40 mu m thick. The composite wires exhibit soft magnetic behavior and the giant magneto-impedance effect. The amplitude of the giant magneto-impedance at high frequencies is comparable to that of conventional amorphous wires and significantly larger than that of NiFe wires without Cu inner core. Nevertheless, the sensitivity of these wires does not reach the theoretical predictions based on the simple models for composite wires with the axial or circumferential types of magnetic anisotropy.