Optimizing magnetoimpedance of amorphous microwires by nanocarbon-induced magnetic anisotropy

Abstract

Approaches to modulate magnetoimpedance (MI) in amorphous wires mostly include annealing, ion irradiation, glass coating and patterning, which are mainly based on induction of transverse magnetic anisotropy. Here, through modulating the magnetization distribution across the wire and outer magnetic shell/ inner core ratio, enhanced magneto- and stress-impedance sensitivity were obtained. Such modulation was achieved by coating a Co-based melt-extracted wire with carbon nanotubes (CNT) and graphene oxide (GO) which induced different level of stresses allowing the increase in outer domain shell volume with helicoidal/circular-type magnetic anisotropy in expense of the axially magnetized inner core. Moreover, through controlling nanocarbon thickness, we demonstrated the validity of high frequency impedance measurements to map the magnetic microstructure across the wire and reveal the core–shell interaction and its contribution to MI. The improvement in transversal anisotropy was evidenced by a drastic increase in MI effect from 170% at 10 MHz for uncoated wire to 400% and 300% for CNT and GO-coated wires, respectively. Finally, by developing a planar model with a four-layer structure, the main features of MI curves were reproduced in the simulated curves. Our results establish a simple platform for the design of microwave materials towards a wide range of sensing applications.