Electromagnetic Properties of Fe50Co50/Cu Granular Composite Materials Containing Flaky Particles

Electromagnetic properties of Fe50Co50/Cu hybrid granular composite materials containing flaky Fe50Co50 particles and flaky Cu ones have been studied in the RF to microwave frequency range to realize the double negative (DNG) material. The electrical percolation along the dispersed Cu particle chains takes place at the critical Cu particle volume fraction phi(c_Cu) = 0.07; the sigma(ac) value of composites with phi(c_Cu) and above was more than 10(-1) S/cm. The negative permittivity caused by the low-frequency plasma oscillation of conduction electron in percolated Cu particle chains was observed above phi(Cu) = 0.08; the hybrid composites with phi(Cu) >= 0.08 are in the low-frequency plasmonic state. Meanwhile, the negative permeability due to the magnetic resonances was obtained above phi(Cu) = 0.10. Therefore, in the Fe50Co50/Cu flaky particle composites with phi(Cu) >= 0.10, the DNG characteristics were realized by the low-frequency plasma oscillation and magnetic resonances in the RF to microwave frequency range. In the Fe50Co50/Cu flaky particle composites, the DNG spectrum was observed at relatively low Cu particle content and the DNG frequency band becomes broad compared to the Fe50Co50/Cu hybrid composites containing spherical or arborized shape particles.