Effect of rare-earth elements microalloying on the glass-forming ability and soft magnetic properties of FeCoSiBCuRE (RE = Sc and Y) amorphous/nanocrystalline alloys

The effects of rare-earth (RE) elements microalloying on the glass-forming ability (GFA), thermal stability, and soft magnetic properties of FeCoSiBCuRE (RE = Sc and Y) amorphous/nanocrystalline alloys have been systematically investigated. Substituting Nb with 3 at. % Sc or Y significantly improved the GFA, enabling the formation of fully amorphous even at Fe contents up to 84 at. %. The addition of Y or Sc induces extra crystallization peaks of the metastable Fe₃B phase, with crystallization temperatures of 850∼860 K for Y-microalloyed alloys and 896 K for Sc-microalloyed alloys. Furthermore, the annealing temperature windows were reduced by 87∼106 K and 32 K, respectively, and consequently thermal stability was weakened. The coercivity (H_c) of the alloy increased sharply after crystallization annealing, owing to the premature precipitation of the hard magnetic Fe₃B phase and increased grain size. In contrast, stress‑relief annealing below the crystallization temperature produced a predominantly amorphous structure with exceptionally low H_c. Among the compositions studied, (Fe_0.8Co_0.2)₈₃Si₁B₁₂Cu₁Sc₃ alloy exhibits the most favorable magnetic properties, achieving a high saturation magnetic flux density (B_s) of 1.66 T and an ultralow H_c of 0.92 A/m. This outstanding performance is attributed to RE‑induced melt purification, improved ribbon surface quality, the elimination of domain‑wall pinning sites, and the formation of a uniaxially induced magnetic‑domain structure.