Study On Giant Magneto-impedance Effect In Composite Wires With Insulator Prepared By Magnetron Sputtering

Ni₈₀Fe₂₀/Cu and Ni₈₀Fe₂₀/SiO₂/Cu composite wires were prepared by RF magnetron sputtering.The wires Were spun during sputtering in order to obtain uniform coatings.The thickness of each layer was controlled by the sputtering time. The influence of the Ni₈₀Fe₂₀ and SiO₂ thickness on the conventional GMI and resonant GMI effect were investigated.We also have studied the GMI effect of Ni₈₀Fe₂₀/Cu composite wire connected with a capacitor in series or in parallel.The main contents and results are as follows:1.Ni₈₀Fe₂₀/SiO₂/Cu composite wires with different thickness of Ni₈₀Fe₂₀ or SiO₂ were prepared,the conventional GMI effect was studied,the results showed that:(1) GMI effect were enhanced significantly with appropriate thickness of the insulator,the optimum insulator thickness was about 5.25μm when the diameter of the Cu core and the thickness of the magnetic layer were controlled at 60μm and 5.25μm,respectively.(2) There is a critical driving current for the measurement of the GMI effect.The MI curve changed from a single peak to monotonic decline with the external magnetic field when the driving current exceeds 20 mA.(3) When the insulator thickness was controlled at 3.75μm the best MI effect was obtained in the composite wires with the magnetic layer thickness of 2.55μm, and the corresponding sensitivity can reach 121%/Oe.2.Resonant GMI was obtained when the Ni₈₀Fe₂₀/Cu composite wire was connected with a capacitor in series or in parallel.The LC resonance GMI effect in the Ni₈₀Fe₂₀/SiO₂/Cu composite wires was also studied:(1) For Ni₈₀Fe₂₀/Cu composite wire the resonant frequency moved to the low-frequency with the increasing of the capacitance,and the maximum MI ratio increases firstly and then decreases with the capacitance value.(2) A novel measurement method was used to study the resonant GMI effect in Ni₈₀Fe₂₀/SiO₂/Cu composite wires with different insulator thickness.We found that the resonant frequency moved to the high-frequency and the maximum MI ratio decrease monotonous with the increasing of the insulator thickness.(3) The resonant MI effect have been studied in Ni₈₀Fe₂₀/SiO₂/Cu composite wires with different thickness of the magnetic layer,the results showed that the resonant frequency decrease firstly and then increase with the increasing thickness of the magnetic layer,and the maximum MI has inverse trend.