GIant magneto-impedance effect of magnetron sputtered Ni ₈₀Fe₂₀/Cu Composite Wires

In this work, Ni₈₀Fe₂₀/Cu composite wires of length 50 mm, consisting a Cu core of diameter 100 μm, coated with a layer of Ni₈₀Fe₂₀, were produced by RF magnetron sputtering. To obtain a uniform coating, the wires were spun during sputtering by a homemade system. The results showed that the spinning speed might affect the maximum MI ratio and the magnetic properties. The MI ratio of the sputtered wires increases with the wire spinning speed in the magnetron sputtering. The film thickness had a significant effect on the magnitude and the optimum frequency of the giant magneto-impedance effect. The maximum MI ratio can reach about 247.4% for the specimen with a Ni₈₀Fe₂₀ coating thickness of 2.81 μm at 400 kHz. This large MI effect, obtained at such low frequency range, was correlated with the electromagnetic interaction between the inner core and the magnetic coating.