Effect of Joule Heating on GMI and Magnetic Properties of Fe-rich Glass-Coated Microwires

Abstract

Amorphous ferromagnetic glass-coated microwires present various properties suitable for technological applications, such as great magnetic softness, ultra-fast magnetization switching and domain wall propagation, inductive heating capabilities or Giant Magnetoimpedance, GMI, effect [1, 2]. Thus, they have been widely studied in the past few years [1].As-prepared Fe and Co based microwires differ in some of these properties. Fe microwires are observed to present magnetic bistability and rather low GMI values, while Co ones possess nearly non-hysteretic magnetization curves and higher GMI [1], making the latter a more attractive candidate for GMI related technologies.However, Co is a critical raw material, making Fe-based microwires preferable for large scale applications. Thus, search of appropriate postprocessing for magnetic softness and GMI improvement is essentially relevant. Among the prospective methods allowing these goals are stress-annealing and Joule heating. As the latter is more effective for tuning of GMI in Co-rich microwires [1], systematic studies of Joule heating on magnetic properties and GMI of Fe-rich ones are scarce.Accordingly, influence of Joule heating on magnetic properties and GMI effect of Fe75B9Si12C4 glass-coated microwires was studied. The GMI ratio, ΔZ/Z, is defined as:ΔZ/Z = [Z(H) - Z(Hmax)] / Z(Hmax)A decrease in coercivity of Joule heated samples is observed, while hysteresis loop maintain rectangular shape (Fig 1). However, a remarkable increase in ΔZ/Z is observed (Fig 2).Observed GMI ratio improvement has been discussed considering magnetic anisotropy by induced magnetic field during Joule heating and internal stress relaxation. Remarkable GMI effect improvement observed in Joule heated Fe-rich microwires, along the fact that Fe is a more common, cheap metal than Co, makes them suitable for magnetic sensor applications.  Fig. 1. Hysteresis loops of Fe75B9Si12C4 microwires Joule heated at 20mA for different times. Inset: coercivity dependence on annealing time.  Fig. 2. GMI ratio of as-prepared (a) and Joule heated for 3min (b) Fe75B9Si12C4 microwires measured at different AC frequencies.