Effects of annealing on the structure and magnetic properties of Fe–Si–Cr flakes and composite sheets

Abstract Gas atomized Fe–Si–Cr powder was used in the application of a bypass sheet in near field communication. The powder was ball-milled, annealed at different temperatures and then manufactured to the sheet. Changes in microstructure and magnetic properties were investigated by XRD, VSM and an impedance analyzer. The as-milled Fe–Si–Cr flake consisted mainly of disordered A2 and ordered B2 phases while the atomized powder consisted of A2, B2 and DO 3 phases. Increases in the annealing temperature caused the formation of a DO 3 phase. At temperatures higher than 923 K, the final flake consisted of only A2 and DO 3 phases. Grain size increased abruptly from 823 K, while the size of the DO 3 phase increased rapidly from 623 K. Coercivity of the flake decreased after annealing, with the lowest coercivity obtained after 923 K annealing while saturation magnetization showed a minimum value of 928 kA/m after 523 K annealing. Sputtered Fe–12%Si films showed a highest electrical resistivity value of 191 μΩ·cm after 623 K annealing while the resistivity of Fe–4%Si sputtered films decreased almost linearly with annealing temperature. Therefore it could be concluded that high permeability of the 623 K sheet at 13.56 MHz and low permeability of the 923 K sheet at 80 MHz were due to the high resistivity as well as nanostructure of the 623 K flake.