Enhancement of giant magnetoimpedance effect of electroplated NiFe/Cu composite wires by dc Joule annealing

Abstract

The influence of dc Joule annealing of electroplated Ni80Fe20/Cu composite wires on their giant magnetoimpedance (GMI) effect is presented in this article. Successive thermal treatments by dc Joule annealing with the current density ranging from 2.4 to 9.6×108 A/m2 were applied to the composite wires for a fixed annealing time of 1 min to release the residual stresses in the plated NiFe layer. The results showed that the magnetoimpedance (MI) effect of the composite wires can be greatly enhanced by dc Joule annealing. For electroplated 1.5 μm of the Ni80Fe20 layer on a copper wire of 20 μm diameter, the optimum annealing current density was found to be 7.2×108 A/m2 and from such annealing the MI ratio was increased from 637% to 1110%, a 74% increment. The optimum ac driving frequency for the GMI effect of the annealed wires under the influence of the annealing conditions in relation to the skin effect and permeability variation in the wires was investigated and discussed. The optimum procedure of dc Joule annealing and the cooling rate against the MI ratio of the annealed wire were also investigated. The results showed that stepped annealing is better than single step annealing and the lower the cooling rate the higher the MI ratio.

Giant magnetoimpedance effect of ac‐dc Joule annealed electroplated NiFe/Cu composite wires

“…Current annealing owing to generating circumferential magnetic field and Joule heating can release internal stresses, induce anisotropy and grow crystal grains. Improvement of MI properties in NiFe/Cu microtubes by proper choice of dc annealing parameters has been reported by some authors [5,12]. In this work, we investigate the influence of ac-dc Joule annealing on GMI response of NiFe/Cu microtubes.…”

“…Heterogeneous materials reveal a superior GMI response than homogeneous materials. It has been shown that among the samples with the same magnetic characteristics, the composite tubes can show the highest magnetoimpedance effect [5]. The origin of GMI in composite microtubes unlike the homogeneous materials does not lie in classical skin effect, and variation in the penetration depth induced by the applied static magnetic field plays no direct role.…”

Magneto-Impedance Effect of Composite Wires Prepared by Chemical Plating under DC Current

“…In previous study [13,22], GMI effect can be enhanced by Joule annealing which induces circumferential magnetic domain. The corresponding annealing current ranges from several hundred milliamperes to several amperes.…”

“…Commonly, the composite wires were fabricated by magnetron sputtering [11], electroplating [12][13][14][15][16], chemical plating [17], or MEMS technique [18]. However, the GMI sensitivity of the composite wires is not high since their magnetic structure cannot be well controlled by these methods.…”

“…It is evident that the highest MI ratio was obtained when pH value is 8.4. The optimal pH value is much higher than that of electroplating method [13][14][15][16]22]. The pH value was kept at 8.4 in the following CPUDC method.…”