Stress-dependent magnetoimpedance in Co-based amorphous wires and application to tunable microwave composites

A novel aspect of the magnetoimpedance (MI) in wires that is of current, research interest arises out of unique electromagnetic properties of the composite materials, the dielectric matrix of which is filled with ferromagnetic wires. It has been demonstrated that the microwave effective permittivity of composite materials containing Co-based amorphous wires has a strong dependence on wire magnetic structure which can be changed by the external magnetic field or stress. To avoid the use of the dc bias field, a special anisotropy, namely nearly axial for λ < 0, is required. Such a "reverse" anisotropy seems to be quite unusual; however, as it was reported recently it could be established by special annealing treatments. In this paper, the nearly axial anisotropy in CoMnSiB glass-coated wires with the metallic core diameter d of 10 microns was induced during annealing a wire mounted on a bobbin (170 °C for 20 min). We have demonstrated that the applied tensile stress produces remarkable-transformations in the dc magnetization loops and huge changes in the impedance including GHz frequency range with the MI ratio running into more than 100% for 600 MPa at 0.5-1.5 GHz.