Design of Core‐Shell Structured Magnetic Microwire with Desirable Properties for Multifunctional Applications

Amorphous Co-rich microwire with excellent soft magnetic and mechanical properties produced by melt-extraction technique are emerging as a multifunctional material for a variety of applications ranging from ultrasensitive magnetic field sensors to structural health self-monitoring composites. The residual stress of extraction process often degrades the mechanical characteristics and magnetic softness of as-quenched amorphous microwire. It is a pressing need for enhancing these properties to make the microwire practical for integration into new technologies. Conventional heat treatments at temperature below crystallization may improve the magnetic softness, but usually deteriorate the mechanical characteristic due to crystallization. Therefore, to address this problem, a multi-step direct current annealing (MSDA) technique uniquely produces innovative nanocrystal-core/amorphous-shell structure directly from as-quenched amorphous microwire (Co_68.15Fe_4.35Si_12.25B_13.25Zr₂). This study investigated the relationship between microstructure and mechanical properties of core/shell composite structures. The results demonstrate that by adjusting the current intensity, the density and size of nanocrystals within the core can be optimized, leading to a significant improvement in the soft magnetic and giant magneto-impedance characteristics. In addition, the amorphous shell maintains the exceptional mechanical strength of microwire. This work also offers a new avenue for research into directly constructing innovative core/shell structures from fast-quenched amorphous magnetic materials.