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. 118 emu/g, 6 times of that in Fe71B17(NbYZr)12 (20 emu/g). The structural origin for such significant difference in magnetic performance was investigated by X-ray absorption 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 μB 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 μB in Fe71B17(NbYZr)12. This work emphasizes how the substitution of analogous 4d transition metals induce significantly different magnetism, which sheds lights on the development of new magnetic metallic glasses with both promising magnetic performance and larger glass forming ability.