Magnetoimpedance effect of current-annealed CoNiFe/Cu microtubes

A cobalt/nickel/iron (CoNiFe) magnetic layer was electrodeposited on a 50-μm-diameter non-magnetic Cu wire in a sulphate bath using a constant voltage. Electrodeposited CoNiFe composite wires were submitted to current annealing at 540 mA. It was found that annealing time less than 1 min removes internal stresses produced during fabrication and that annealing times longer than 5 min induce circumferential anisotropy. Non-annealed sample showed a magnetoimpedance (MI) ratio of 412%. A maximum MI ratio of 583% was obtained after 1 min of current annealing.