Electromagnetic properties of Co flaky particles prepared via ball-milling method

• Flaky Co particles with various aspect ratio were prepared via ball milling in large quantity.
• Coatings containing flaky Co particles present excellent EMA performance in 2–4 GHz band.
• The effect of shape on the permeability and the permittivity was investigated.

Flaky cobalt particles with different aspect ratio were produced with ball-milling method. The phase structure and morphology of the particles were identified by XRD analysis and SEM observation. The static magnetic and electromagnetic properties of the particles were measured and effects of shape, microstructure and filling fraction were investigated. Phase transition from fcc lattice to hcp lattice occur due to the drive of ball-milling is responsible for the largely increased coercivity. Particles with high aspect ratio are found to possess high permittivity and permeability, compelling the frequency of absorption peak to shift to low frequency. Coatings using cobalt particles milled for 20 h as fillers present a RL peak of −33 dB at 8 GHz at the thickness of 2.5 mm together with a broad effective absorbing (RL below −10 dB) bandwidth covering 6–10 GHz.