Stress - and Magneto-Impedance in Co71-xFexCr7Si8B14 (x = 0, 2) amorphous ribbons

Systematic measurements of stress impedance (SI) and magneto-impedance (MI) have been carried out using Co-rich amorphous ribbons of nominal composition Co71-xFexCr7Si8B14 (x = 0, 2) at various excitation frequencies and bias fields and at room temperature. The impedance, Z, for both the samples was found to be very sensitive functions of applied tensile stress (up to 100MPa) exhibiting a maximum SI ratio as much as 80% at low frequency ~ 0.1MHz. The nature of variation of impedance, Z, changes with the excitation frequency especially at higher frequencies in MHz region where it exhibits a peak. Magnetization measurements were also performed to observe the effects of applied stress and magnetization decreases with the application of stress confirming the negative magnetostriction co-efficient of both the samples. Both the samples exhibited negative magneto-impedance when the variation of Z is observed with the applied bias magnetic field, H. Maximum MI ratio as large as 99% has been observed for both the samples at low fields ~ 27Oe. The impedance as functions of applied magnetic field, Z(H), decreases with the application of stress thus making the MI curves broader. Based on the electromagnetic screening and magnetization dynamics and incorporating the Gilbert and the Bloch-Bloembergen damping and stress dependent anisotropy, the SI has been calculated and is found to describe well the stress and field dependence of impedance of the two samples.