Interplay of stress, temperature, and giant magnetoimpedance in amorphous soft magnets

Abstract

Giant Magnetoimpedance (GMI)-based sensing devices have attracted attention from both academia and industry due to their low cost, flexibility, and excellent sensitivity. Potential applications range widely from current and stress sensors, navigation systems, magnetic recording, to more demanding ones such as field sensors for deep drilling and oil fracking at elevated temperature. To realize the latter, the temperature dependence of GMI effect must be well understood. Herein, we report a study on the GMI effect in a Cobalt-based amorphous microwire under temperature cycles between 20 °C–560 °C. The GMI ratio was observed to decrease from 126.1% at 20 °C to 68.5% at 230 °C, rapidly drop at ∼290 °C and reach a near zero value above 320 °C in the first half of the measurement where the temperature was increased. Upon cooling down from 560 °C to 20 °C, the GMI ratio exhibits little variation at ∼95% in the 260 °C–20 °C regime. Similarly, the anisotropy-temperature profile was also observed to change irreversibly during the temperature cycle. Previous work has found the correlation between internal stress, anisotropy, permeability, and GMI effect. We hypothesize that irreversibility in GMI-temperature and anisotropy-temperature profiles stem from internal relief in the amorphous structure, which is locked in during the rapid cooling. In the subsequent temperature cycles, the GMI-temperature and anisotropy-temperature profiles show little variation, thus supporting the notion that the internal stress relief is complete after the first temperature cycle.