Role of rare earth elements addition in enhancing glass-forming ability and magnetic softness of a Co75B25 metallic glass: Theoretical prediction and experimental verification

The effects of light/heavy rare earth (L/HRE) elements addition on local atomic structures, glass-forming ability (GFA), and soft magnetic properties of a Co75B25 metallic glass (MG) were comprehensively investigated using theoretical prediction and experimental verification methods. Ab initio molecular dynamics (AIMD) simulations based on density functional theory (DFT) calculations revealed that the Co-RE-B (RE = La, Sm, Gd, and Y) MGs exhibit unique structural heterogeneities, with B-centered prism units dominating the local atomic structures. Compared to the Co-LRE-B (LRE = La and Sm) MGs, the Co-HRE-B (HRE = Gd and Y) MGs possess stronger bond strengths and higher fractions of icosahedral-like (ico-like) units, leading to remarkable enhancements in structural stability, fivefold symmetry, atomic packing density, and sluggish diffusion, ultimately resulting in enhanced GFA. Furthermore, the lower magnetic anisotropy energy (MAE) and range of the local loosely packed regions (LLPRs) in the HRE-containing MGs can significantly promote magnetic softness. The theoretical analysis predicts that the MGs containing the HRE possess higher GFA and magnetic softness with the order of Co75B25 < Co71.5La3.5B25 < Co71.5Sm3.5B25 < Co71.5Gd3.5B25 < Co71.5Y3.5B25. These predictions have been successfully verified by the experiments in both local atomic structures and properties, through the in situ high-energy synchrotron X-ray diffraction (HEXRD) characterization, as well as evaluations of thermal and magnetic properties.