Unveiling the role of Y content in glass-forming ability and soft magnetic properties of Co-Y-B metallic glasses by experiment and ab initio molecular dynamics simulations

Abstract

The effects of Y content on glass-forming ability (GFA) and soft magnetic properties of Co75-xYxB25 (x = 0, 3.5, 5) metallic glasses (MGs) were investigated by experiment and ab initio molecular dynamics (AIMD) simulations, and the relationship between local atomic structures and properties was discussed. The GFA and magnetic softness of Co75B25 alloy are improved by 3.5 at.% Y addition in our experiment. By calculating the local atomic structures (pair distribution function, coordination numbers, chemical short-range order, Voronoi polyhedron, structure factor, and the ratio of voids), dynamic behavior, electronic structure, magnetic moment, and magnetic anisotropy energy (MAE), we have found that the local atomic structures of Co-Y-B MGs are dominated by the B-centered prism units, and Y plays a vital role in the formation of the densely packed structures. In particular, the strongest chemical affinity of B-B, Co-Y, and B-Y pairs in Co71.5Y3.5B25 alloy is the critical factor for enhancing GFA and magnetic softness, which improves the degree of atomic packing in the first shell, the viscosity of supercooling melts, the stability of the local atomic structures, and reduces the MAE of the system. However, the excessive addition of Y (5 at.%) leads to a reduction of the GFA and magnetic softness, which may contribute to the highest fraction of deformed body-centered cubic (bcc) structures and the largest size of the medium-range order (MRO) structure in Co70Y5B25 alloy. This study shows a valuable perspective to understand the correlation between local atomic structures and properties of Co-based MGs, and also provides ideas for designing high-performance soft-magnetic MGs.