Giant magneto-impedance effect in NiCoP/insulator/CuBe composite wires

Composite wires CuBe/insulator/NiCoP of 60 mm insulated CuBe core coated with a layer of Ni₅₇Co₃₈P₅ were produced by electroless deposition, and their magnetic properties were studied. The results showed that a good magneto-impedance effect can be obtained at relatively low frequency. The magneto-impedance effect was observed even at 1 kHz, it reaches -3.32%. The maximum GMI ratio of composite wire reached 108% at 300 kHz. In order to improve the soft magnetic properties, then, the samples were annealed at 200°C in N₂ atmosphere. The influence of magnetic layer thickness on GMI was also investigated. The study showed that MI ratio is dependent not only on the value of ΔR/R and ΔX/X but also on the ratio between R and X.