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 (fr) and internal strain (〈ɛ〉) 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 〈ɛ〉, suggesting that 〈ɛ〉 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 〈ɛ〉 in the as-milled nanocrystalline CIPs.