Structural origin of magnetic softening in a Fe-based amorphous alloy upon annealing.

• Upon annealing, the microstructure, not only in short range order but also in medium range order, contributes to the magnetic softness in Fe-based amorphous alloy. • Exchange coupling of homogeneous weak and strong magnetic regions generate excellent magnetic softness. • A configuration with energetically stabilization is formed annealed at optimized temperature, resulting in heating-rate independence of coercivity. The underlying structural origin of magnetic properties is still elusive in Fe-based amorphous alloys. In this study, distinctive soft magnetic properties were developed in Fe 76 Si 9 B 10 P 5 amorphous ribbons through systematic design of annealing process. Combining with synchrotron radiation, high-resolution transmission electron microscopy and first principle ab initio molecular dynamic simulation, it is found that the atomic structural evolution both in short range order and medium range order is responsible for the magnetic softness at proper annealing temperature. In short range, formation of separated and densely coordinated Fe-metalloid clusters is instigated to adapt energy minimization, resulting in strengthening of ferromagnetic exchange interaction locally. In medium range, a homogeneous exchange-coupling from the uniformly strong and weak ferromagnetic regions is generated, which significantly weakens magnetic heterogeneity and leads to the excellent magnetic softness. Our findings may provide an effective/promising pathway to modulate the magnetic properties for Fe-based amorphous alloys, and give a comprehensive and quantitative understanding of the structure-properties relationship in amorphous materials. [Display omitted] [ABSTRACT FROM AUTHOR]