Internal strain dependence of complex permeability of ball milled carbonyl iron powders in 2-18 GHz

A series of the flake-like and sphere-like nanocrystalline carbonyl-iron powders (CIPs) were prepared by high energy ball milling raw CIPs for different times (t). Variations of the structure, morphology, microwave complex permeability, and static magnetization with t for the two kinds of CIPs have been investigated using x-ray diffraction, scanning electron microscopy, vector network analyzer, and vibrating sample magnetometer, respectively. The results show that with prolonging t, the nature resonance frequency (f(r)) and internal strain (<epsilon >) increase monotonously for the sphere-like nanocrystalline CIPs, while those fluctuate for the flake-like nanocrystalline CIPs. These phenomena are in accordance with the increasing fr with increasing <epsilon >, suggesting that <epsilon > suppresses the domain wall displacement and promotes the gyromagnetic spin rotation. As a result, the competition between the domain wall displacement and the gyromagnetic spin rotation can be effectively controlled by <epsilon > in the as-milled nanocrystalline CIPs. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4716028]