Structural tuning for enhanced magnetic performance by Y substitution in FeB-based metallic glasses

Despite the compositional analogue to Fe₇₁B₁₇(NbYZr)₁₂ metallic glass, the Fe₇₁B₁₇Y₁₂ metallic glass has a saturated magnetization of Ca 108 emu g^-1, more than 5 times of that in Fe₇₁B₁₇(NbYZr)₁₂ (20 emu g^-1). The structural origin for such significant difference in magnetic performance was investigated by x-ray absorption fine structure spectra and ab initio molecular dynamics (AIMD) simulations including simulated pair-correlation function (PCF) and Voronoi tessellation. Based on the Heisenberg model of magnetism, the narrow distribution of Fe-Fe bonds with larger distances accounts for a large Fe moment of 2.0 μ _B in Fe₇₁B₁₇Y₁₂, while the broad distribution of Fe-Fe bonds leads to ferrimagnetic couplings which result in the small net Fe moment of 0.45 μ _B in Fe₇₁B₁₇(NbYZr)₁₂. This work emphasizes how the substitution of analogous 4d transition metals induces a significantly different magnetism, which sheds lights on the development of new magnetic metallic glasses with both a promising magnetic performance and larger glass forming ability.