Ultrafast Particle Size Reduction of Fe_73.9Si_15.5Cu₁Nb₃B_6.6 by High-Energy Milling: Nb₂O₅ as a Marker of Permeability Enhancement and Magnetic Hardening

This work is conceived to provide a reproducible and fast method to obtain optimal particle sizes for competitive ultrasoft magnetic applications based on Fe73.9Si15.5Cu1Nb3B6.6-nanostructured particles. In this scenario, partial nanocrystallization of the α-Fe3Si compound is promoted by annealing and subsequent high-energy ball milling processes. The milling is performed in this material, for the first time, by a combination of mixer, vibratory, and planetary ball milling motions. Under these conditions, structural and magnetic properties are tuned as a function of milling time with reduced particle size distributions and maintaining the ultrasoft magnetic character. In addition, drastic electronic and structural changes are observed after a few minutes of milling where saturation magnetization and initial permeability are strongly influenced by the percentage of the α-Fe3Si nanocrystallites formed. Above 30 min of ball milling, the formation of a low concentration of Nb2O5 clusters is detected by confocal Raman microscopy. This identification is essential because the rejection of Nb from the amorphous matrix rich in Fe–Nb–B atoms acts as a marker of the seed mechanism that causes the deterioration of the softness character of these nanostructures. Therefore, on the one hand, this work introduces a successful procedure by combined milling processes to optimize the saturation magnetization and permeability with submicron particle sizes and, on the other hand, the detection of Nb2O5 clusters is implemented as an influential marker on the magnetic properties of these soft nanostructured particles.