Composite Wire Giant Magneto-impedance Effect

In this thesis, the composite wires with two different core layer were prepared on the basis of glass-coated melt-spinning method in combination with electroless deposition and magnetron sputtering. The giant magneto-impedance effect (GMI) properties were investigated. The results show that the electromagnetic interaction occurs between the layer and the layer in sandwiched composite wires, the eddy effect and skin effect play an important role for arising the giant magneto-impedance,. 1 The amorphous microwires of nominal compositions Fe73.0Cu1.0Nb1.5V2.0Si13.5B9.0 were prepared by glass-coated melt-spinning method. Nanocrystalline microwire was obtained by annealing amorphous wires at 570 C for improve its soft magnetic properties. The Giant Magneto-impedance is more sharply in nanocrystalline microwire. In addition, BeCu/NiCoP and BeCu/Insulator/NiCoP composite wires were prepared by electroless plating of a NiCoP layer onto BeCu and insulated BeCu wires, the composite wires were annealed in order to eliminate the stress caused during the process of preparation, the GMI effect on the composite wires are studied. 2 Using electroless deposition, a thin layer of copper was deposited onto the glass-coated microwires, and the composite wires with ferromagnetic core wereproduced. The influence of copper thickness ( 0 m , 1 m , 1 .5 m , 2 m ) on GMI was investigated. Experiment results show that the GMI effect of the wire deposited with a copper layer ( 1 .5 m ) increases at low frequencies and decreases at highfrequencies, because the eddy current was induced by the electromagnetic interactions in the Cu layer, and reacts to ferromagnetic core, as a result, the onset frequency of the MI ratio decrease. Further increasing frequency, the magnetization is damped strongly so the MI ratio decreases. However, the thickness of copper layer equals 2 m , the eddy current increases dramatically, the above-mentioned trend disappears.3 Copper layer was also deposited using magnetron sputtering onto the annealedglass-coated microwires. The GMI effect was investigated with ac driving current flowing through different layer. The result shows that the peak corresponding to the maximum of MI ratio moves towards higher field values with the thickness of copper layer, at the same frequency. The driving current Jo decreases due to the eddy current inside the copper, therefore the compensation field Hm increases, the MI ratio at1MHz is evident when the current flows through both ferromagnetic core and copper layer, the current will flow mainly through the copper layer with larger conductive , the contribution of inductive effect increases for GMI effect at low frequencies.4, The GMI effect of composite wires BeCu/NiCoP and BeCu/Insulator/NiCoP were investigated, the results show that the obvious GMI effect can be observed at lower frequencies. It is because the ac current flows through the inner conductive layer mainly, and the closed outer ferromagnetic layer becomes the main magnetic inductive loop, the onset frequency reduces. In addition, when the conductive layer and the ferromagnetic layer are separated by insulating layer in composite wires, the MI sensitivity of BeCu/insulator/NiCoP is superior to BeCu/NiCoP, owing to the eddy current loss decreases.