Study On Giant Magneto-impedance Effect In Electroless Plated CoNiP/Cu Composite Wires

CoNiP/Cu composite wires were prepared by electroless-deposition on Cu core with 90μm in diameter. The influences of pH values on the structure and component of composite wires and GMI effect were investigated. Furthermore, the GMI effect is enhanced and magnetic sensibility is improved by current annealing, deposition with dc current and adjusting the driving current amplitudes. The main contents and results are included as follows:1. Influences of pH values of plating bath on GMI effect of composite wiresThe CoNiP/Cu composite wires were prepared by electroless-deposition undervarious pH values, and the relationship between GMI effect and pH values were investigated. The results show that the CoNiP/Cu composite wires have amorphous structures in the range of experimental pH values, With the increase of the pH value, the contents of Ni and P in deposited layer increase while the content of Co decreases The variation component and magnetic structure of the deposited layer affect GMI effect of composite wires.2. Influences of current annealing on GMI effect of the composite wiresCurrent annealing was performed on the as-cast CoNiP/Cu composite wires, andthe influence of the amplitudes of current and annealing time on GMI effect were investigated. The results show that the internal stress would be released by heating when annealing current was 1A, which did not change the magnetic structure. When the annealing current is 2A, circumferential magnetic domain structures would be formed. Both internal stress relief and circumference magnetic domain structures can enhance GMI effect of the composite wires. The composite wires annealed under 2A in 120s can reach the maximum GMI ratio of 400% in 80kHz.3. Influences of dc bias circumferential magnetic field in the plating process on GMI effect of composite wireCircumferential magnetic field is generated by dc current flowing Cu wire in the plating process, so the influence of dc bias circumferential magnetic field on the magnetic structure of composite wire and GMI effect is investigated. The results show that circumferential magnetic domain structures would come into being in deposited layer, which show peaks in GMI curve and obvious enhancement of GMI effect. When the biased current is 80mA, the GMI ratio of as-cast composite wires can reach 850%.4. The driving current on GMI effect of composite wireThe influence of the amplitude and the frequency of the driving current on the GMI effect were investigated. The amplitude of driving current changes the driving magnetic field and affects the magnetization process of magnetic layer in composite wire. Therefore, it finally affects the GMI effect and field sensitivity. The results show that the GMI effect is enhanced and the field sensitivity increased with the current increasing, and the shape of GMI curve changes from two peaks into single peak.