Giant magnetoimpedance effect in a positive magnetostrictive glass-coated amorphous microwire

Abstract

The giant magnetoimpedance (GMI) effect in positive magnetostrictive glass-coated amorphous ${\mathrm{Co}}_{83.2}{\mathrm{Mn}}_{7.6}{\mathrm{Si}}_{5.8}{\mathrm{B}}_{3.3}$ microwire has been studied as a function of a dc magnetic field $\ensuremath{-}140l{H}_{\mathrm{dc}}l140\mathrm{Oe}$ and frequency $0.1lfl12.85\mathrm{MHz}.$ A maximum change of 43% in the MI of the as-quenched sample has been observed around 5 MHz frequency. Heat treatment of the sample by passing a dc current of 50 mA through it enhances the MI value to a large extent (maximum change \ensuremath{\sim}94%) by increasing the outer domain volume and inducing a transverse anisotropy. On the other hand, application of an external tensile stress reduces the GMI value by increasing the inner core domain and developing an axial anisotropy. In an as-quenched sample, the maximum value of MI is observed at ${H}_{\mathrm{dc}}\ensuremath{\sim}0$ when measured at frequency $fl8\mathrm{MHz}$ beyond which a two peak MI profile is seen. The heat-treated sample shows this two peak behavior from a much lower frequency (below 1 MHz) and additional peaks at ${H}_{\mathrm{dc}}\ensuremath{\sim}0$ for $fg10\mathrm{MHz}.$ Asymmetry in the MI peaks of a microwire has been produced by passing a dc current through the sample during impedance measurement. The magnetization of the as-quenched and heat-treated samples has also been studied to understand the domain structure and magnetoimpedance results.