Characterization of structures and novel magnetic response of Fe87.5Si7Al5.5 alloy processed by ball milling

The water atomized Fe87.5Si7Al5.5 (Wt.%) alloy was processed by a high-energy planetary ball-milling. The characterization of morphology, microstructure, and electromagnetic properties were measured by scanning electron microscope (SEM), X-ray diffractometer, vibrating sample magnetometer (VSM), vector network analyzer and the first principle method. The analysis results showed that the powders shape became flaky from fusiform. The powders showed a reduction of the average grain size and the increase of the internal strain, and then presented an adverse variation trend after 55 h milling. The powders that milled 10 h had the largest saturation magnetization M-S (131 emu/g). The value mu' of the powders decreased with increasing milling time at relatively lower frequency (2-8 GHz), but opposite variation tendency happened at higher frequency (8-18 GHz). Also, only short time milling can enhance the value of mu '' in the test frequency. The powders after 10 h milling showed excellent microwave absorption (RL < -10 dB) at the frequency 9.0-15.6 GHz and the absorption peak shifted regularly to the high frequency as the increased milling time. Furthermore, the effect of charge exchange between the Fe and Si on the saturation magnetization in the ball-milling process was also investigated by using density functional theory (DFT) of first principle. (C) 2012 Elsevier B. V. All rights reserved.