Coexistence of gyromagnetic resonance and low frequency plasmonic state in the submicron Ni granular composite materials

Abstract

Relative complex permeability and permittivity spectra of submicron Ni granular composite materials have been studied from RF to microwave frequency range for realization of the negative permittivity and permeability spectra. The Ni particles are spherical in shape with the average diameter of 170 nm; the electrical conductivity of compacted particles shows a semiconductive property. From the variation of conductivity with particle content, it was found that the Ni composite material indicates an electrical percolation at 56.0 vol. % where the conductivity shows an abrupt increase. Above the percolation threshold, a positive permittivity spectrum with conductive loss was observed up to 65.7 vol. %; the low frequency plasmonic state with the negative permittivity spectrum was found at the particle content of 66.1 vol. %. A negative permeability spectrum caused by the gyromagnetic spin resonance was also observed in the particle content above 60 vol. %. The coexistence of negative permittivity and permeability spectra was realized in the 66.1 vol. % Ni granular composite. The negative permeability spectrum was induced by the external magnetic field in the percolated 57.5 vol. % sample; a ferromagnetic resonance type permeability dispersion is enhanced by the external field.