Electric And Magnetic Properties In Magnetic Granular Composite

Granular composite refers to a new kind material containing small particles embedded randomly in a host. The granular composites made of different materials often exhibit interesting physical phenomena and can be widely used in different application fields. So, it becomes a popular thesis and many theoreticians and experimentalists are interested in investigating such granular composites.In this thesis, we study the magnetic granular composite consist of metallic magnetic particles embedded randomly in a nonmagnetic and insulated host. With the aid of the effective medium theory and the dynamic effective medium theory, we concentrated on permeability and permittivity spectra of the metallic magnetic granular composites and left-handed characteristic of metallic magnetic nanoscale granular composites and so on.We investigated the granular composites consist of the single-domain ferromagnetic particle with uniaxial anisotropy, suppose all particle have the same size. We derived the average susceptibility of the single-domain magnetic particles. Take into account the particle size and permittivity and permeability,on a base of the effective-medium theory, with the aid of the dynamic EMA method, we investigated permeability and permittivity spectra of the metallic magnetic granular composites. The calculation result showed that, in the granular composites consist of nonmagnetic metallic particles embedded randomly in a magnetic and insulated host, the metallic particles can excite the resonance of the magnetic particles in high frequency and so on.When the size of particle much smaller than the wavelength of the electromagnetic wave, we obtained the effective permittivityεeand the effective permeabilityμe via the Bruggeman formula in finite frequencies , along with the wave vector k and the average poynting's vector S . According to the electromagnetic knowledge, When a plane wave ( the wavelengthλR of the magnetic particle radius ) propagates in the composite system, in some frequency range , we found that the scalar product of the wave vector k and the average poynting's vector S at the finite frequencies is less than zero , namely Sω? Re( k) < 0 , therefore the composite may show the so called left-handed characteristic in this frequency range. When the damping coefficient of the composites diminished, there are a negative effective permittivity and simultaneously a negative effective permeability in the composites near the frequency of the magnetic resonance, the other way round the magnetic resonance weaken, the negative effective permittivity will be absent,so the left-handed characteristic disappeared in the composites in this frequency range.