Amorphous magnetism in Fe80MxB20-x (M = C, P, Si, Ge; x = 5, 10, 15) alloys: A first-principles computational study

The incorporation of metalloids modulates the soft magnetic properties of amorphous alloys, including their permeability and coercivity, by tailoring their atomic structure and electronic interactions. Related research has always been a popular field. Although relevant theories have provided explanations, the correlation between the structure and magnetism is still not clear. In this work, a systematic first-principles molecular dynamics study was conducted to investigate the effects of metalloids (C, P, Si, Ge) on the soft magnetic properties of FeB-based amorphous alloys. The results indicate that the Voronoi polyhedra centered on Fe atoms are predominantly distorted icosahedra, with a minority of regular icosahedral configurations. In contrast, polyhedra centered on P, Si, and Ge atoms are primarily distorted icosahedral structures, whereas those around C and B atoms are triangular prisms. The magnetic moment of Fe atoms in the amorphous alloy gradually increases when Si and Ge substitute for B atoms, whereas it decreases with C and P substitution. This calculated trend aligns well with the experimental observations. The magnetic moment of a central Fe atom exhibits strong coordination dependence: it increases proportionally with the number of neighboring Fe atoms but decreases systematically with increasing coordination by metalloids. This anti-correlation reflects the competitive interplay between ferromagnetic coupling and hybridization-driven moment reduction mechanisms. These results provide essential data for both the development of soft magnetic properties in amorphous alloys and fundamental research in this field.