Electronic-structure origin of the glass-forming ability and magnetic properties in Fe-RE-B-Nb bulk metallic glasses

(Fe0.71RE0.05B0.24)96Nb4 (RE = Gd, Tb, Ho, Er, Tm) bulk metallic glasses (BMGs) were found exhibiting excellent glass-forming ability (GFA) with critical diameters ranging from 3.5 to 6.5 mm, and high compressive fracture strength larger than 4300 MPa. Moreover, they displayed good soft-magnetic properties with saturation magnetic flux density of 0.71-0.87 T, coercive force of 1.23-39.76 A/m and effective permeability of 1500-12,740 at 1 kHz. X-ray photoelectron spectroscopy was performed to clarify the origin of the excellent GFA from the viewpoint of electronic structure. It was found that the Tm doped alloy displayed unique electronic structure including the deepest core-level binding energy, the most numerous RE-B bonds and the minimum density of states near the Fermi level, making this alloy the best glass former. The various trends noticed in the magnetic properties were ascribed mainly to the differences in the magnetic anisotropy and magnetic moment of RE elements.