Executive Summary : | Metamaterials show intriguing properties, i.e. a negative permittivity and a negative permeability in the same frequency range, which are interesting for a wide range of microwave applications. Initially identified in metamaterials composed of split ring resonators, it was shown recently that composites from a ferromagnetic insulator and a metal can exhibit also Double negative materials (DNM) behaviour, if the volume fraction of the metal is just above the percolation threshold. The synthesis of this kind of composite DNM being less costly, this project aims to explore new DNM composites based on ferrite composites for the application in the low GHz range. In these composites, the ferrimagnetic insulating component allows for the negative permeability by domain wall and gyromagnetic spin resonances, while the negative permittivity stems from the plasma resonances in the metallic component. The main ferrites used in this project will be Ni-Zn ferrites due to their soft magnetic behaviour, doped with different metals as Co, In or Cu. Therefore, this project aims to develop and characterize new DNM composites for microwave applications. The main objective of the proposal is to achieve double negative materials for application in the low GHz frequency range. This objective will be pursued in the project by the given experimental approach. First of all, composite materials obtained by citrate precursors will be studied, especially those of soft magnetic materials allowing for high permeability, like Ni-Zn based ferrites doped with Co, In and Cu. Different parameters like pH, sintering temperature, heating rate, pressure etc will be optimised so as to lower the value of damping factor, α of the synthesized magnetic particles. The best compositions among Ni-Zn ferrites will be doped with Co, In and Cu. Cobalt is useful for increasing magnetocrystalline anisotropy and hence shifts the resonance frequency to the targeted frequency region between 1 and 3 GHz. Indium is useful to increase µ' and Copper to lower the sintering temperature and to enhance the densification. Metallic granular (Cu/Ag) based composites in which the metallic components are randomly distributed will be fabricated. The metallic components will be doped in the matrix, and the role of the value of the ratio Cf /Ce (with C and C are above the percolations magnetic and conducting thresholds, respectively) will be examined. Metamaterials can exhibit special properties with both negative permittivity and permeability and refractive index, consisting of sub-wavelength resonators. |