Negative permittivity in Fe–Si–Ni/epoxy magnetic composite materials at high-frequency

The radio frequency permittivity and permeability spectra of Fe–Si–Ni/epoxy magnetic composite materials were investigated in detail. A relaxation frequency dispersion of permittivity has been observed for the composites below percolation threshold, and tunable negative permittivity due to the plasma oscillation of delocalized electrons in interconnected Fe–Si–Ni has been obtained in the composites above but still near percolation threshold. The realization of negative permittivity in Fe–Si–Ni/epoxy composites can be applied for the electromagnetic shielding materials. •We proved the negative permittivity can be tuned by adjusting the Fe–Si–Ni content.•Plasma oscillation of delocalized electrons is contribute to negative permittivity.•The negative permittivity behavior can be fitted well by Drude model.