Mössbauer studies on the shape effect of Fe_84.94Si_9.68Al_5.38 particles on their microwave permeability

Ball milling for long time (such as 10, 20, and 30 h) can transform Fe_84.94Si_9.68Al_5.38 alloy powders with irregular shapes into flakes. X-ray diffraction (XRD) and Mössbauer measurements have proven that the unmilled particles and the flakes obtained by milling for 10 h have the same D0₃-type superlattice structure. The flakes obtained by milling for 20 h and 30 h have the same disorder α-Fe(Si, Al) structure. There are more than 6 absorption peaks in the transmission Mössbauer spectra (TMSs) for the particles with D0₃-type superlattice structure, which can be fitted with 5 sextets representing 5 different Fe-site environments. However, only 6 TMS absorption peaks have been found for particles with a disorder α-Fe(Si, Al) structure, which can be fitted with the distributions of Mössbauer parameters (Bhf, isomer shift). The TMS results show that the flaky particles have a stronger tendency to possess the planar magnetic anisotropy. As the result, the flakes have larger microwave permeability values than particles with irregular shapes. The conversion electron Mössbauer spectra (CEMSs) also show the significantly different Fe-sites environments between the alloy surface and the inside.