Spinel ferrite flakes are prepared for use as fillers in electromagnetic (EM) composites. EM attenuation composites with the flaky fillers exhibit greatly enhanced high-frequency magnetic properties and attenuation properties. The complex permeability, μ'r,o and μ"r,max, is enhanced by above 300%, and the relative attenuation bandwidth Wp is increased by 40%, as compared to those for composites with conventional spherical fillers. Wp achieves 80% of the theoretical maximum relative bandwidth. The composites with the flaky fillers are powerful and potential candidates as EM attenuation materials with broad bandwidth at microwave frequency.