Influence of Fe doping and FeNi-layer thickness on the magnetic properties and GMI effect of electrodeposited Ni_100-xFe_x/Cu (x = 0–95) wires

A systematic study has been performed by the influence of Fe doping and FeNi-layer thickness on the giant magnetoimpedance (GMI) effect of electrodeposited Ni100-xFex/Cu (x = 0–95) composite wires. Results obtained show that there is a correlation between the structure, soft magnetic properties and the GMI effect. Among the compositions investigated, the largest MI ratio is achieved for Ni44Fe56/Cu as a result of it having the softest magnetic property (i.e. the lowest coercivity), which arises from the smallest nanograin size. As the NiFe-layer thickness (t) increases from 1 to 27.4 µm, the GMI ratio initially increases, reaches a maximum of 110% at t = 27.4 µm and then decreases for t > 27.4 µm. Interestingly, GMI curves show a single-peak feature for wires with t <20 µm, but a double-peak one for wires with t ≥ 20 µm. This indicates that there is a formation of a circular domain structure with a well-defined circumferential anisotropy in the NiFe magnetic layer of the wires with t ≥ 20 µm. This in turn results in a great improvement in the GMI effect of these wires.