Microwave Permeability Change of FeCo Nanocrystalline During High Energy Ball Milling

The microwave magnetic properties of the ball milled FeCo particles were investigated as functions of ball milling time (t) using microwave electromagnetic parameters analysis techniques. The results show that the imaginary part of intrinsic dynamic permeability (μ_i) of the ball-milled particles is much bigger than that of raw powders. μ_i strongly depends on t and exhibits several slightly damped ferromagnetic resonances. These phenomena are in qualitative agreement with the formation of the corresponding microstructure or the Aharoni’s model of non-uniform exchange resonance modes. The present microwave permeability behavior indicates that nanocrystalline materials with the same grain size may exhibit different properties that depend upon the microstructure, which provides a possibility for manufacturing high performance microwave absorber.