Preparation and Characterization of Fe-Based Amorphous Soft Magnetic Flakes for High Performance Magnetodielectric Inductors

Flake-shaped FeSi-P alloy particles with high aspect ratio were prepared by ball milling 25 um spherical amorphous powders that boasted one of the world's highest saturation magnetic flux densities at 1.5 T, and ultra-low coercivity below 0.5 Oe. We demonstrate that the aspect ratio of the flakes, as well as the magnetic properties, can be control by the milling parameters, such as milling time, speed, and the composition of the milling balls. The balls-to-powder ratio was varied between 2.6-10, balls diameter between 3-10 mm, and milling time between 1-25 hours. To avoid oxygen exposure, the powders were handled in argon atmosphere in a glove box, milled in toluene, and subsequently dried in vacuum. The maximum aspect ratio of the flakes exceeded 70: 1, and was achieved after milling for 20 hours with 6mm balls. The samples were thoroughly characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA), and vibrating sample magnetometery (VSM). It was determined that after the milling, the coercivity Hc increased from 0.5 Oe to 39.0 Oe, and the saturation flux density Bs decreased from 1.5 T to 1.3 T. The flakes were subsequently annealed in flowing argon for 1 hour between 300-450 C. The coercivity and saturation flux density initially improved with temperature, and respectively reached 18.8 Oe and 1.4 T at 375C. The crystallization occurred at higher temperatures, and magnetic properties gradually declined.