Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains xiii, 96 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 86-87).

I performed first principles studies of the site occupancy and magnetic properties of zinc-tin-substituted strontium hexaferrite by using density functional theory. In this study, I determined the site preference of zinc and tin atoms when they are restricted to occupy the same sublattice in strontium-hexaferrite. I found that Zn and Sn atoms prefer to replace Fe ions at 2a sublattice under this restriction and caused the saturation magnetization to decrease.

published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy

No description available.

No description available.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science WITS University, Johannesburg, 2013 / Occurring parallel to the developments in imprinting technology are magnetic materials which are being applied increasingly in environmental remediation, medicine, biotechnology and many other fields. Combining the imprinting effects of the polymer and nano magnetic particles yields composite materials which are both selective to the template and magneto responsive for easy polymer removal from aqueous solutions. In this study, magnetic ion imprinted polymers with high recognition for uranyl ion (UO2 2+) in the presence of competing ions were synthesized by bulk and precipitation polymerizations. The uranyl template was removed from the magnetic polymer matric by 1M HCl and 1M NaHCO3 leachants to form cavities which were complimentary in shape and size to the template. Full characterization of the magnetite and magnetic polymers was achieved by use of the following characterization techniques: Raman spectroscopy (RS), Transmission electron microscopy (TEM), Energy dispersive spectrometry (EDS), Powder X-ray diffraction (PXRD) analysis, Brunauer, Emmett and Teller (BET) analysis, Ultraviolet visible (UV-vis) spectroscopy, Fourier-transform infrared (FTIR), Thermo-gravimetric analysis (TGA), Carbon, hydrogen, nitrogen and sulphur (CHNS) analysis, Diffuse reflectance spectroscopy (DRS) and Atomic force microscopy (AFM). Parameters which were optimized included sample pH, which gave an optimum value of 4. Magnetic IIP and NIP amounts which gave maximum adsorption capacities were found to be 50 mg for both of these adsorbents. The optimum contact time was found to be 45 minutes. The performance of all magnetic ion imprinted polymers (IIPs) was expectedly superior to that of the corresponding non imprinted polymers (NIPs) in all adsorption studies. The first rate constant (k1) and correlation coefficient (R2) values evaluated for the pseudo first order were found to be between 0.048-0.093 min-1 and 0.602-0.991 min-1, respectively. For the pseudo second order, second rate constant (k2) and correlation coefficient (R2) were found to be between 0.273- 0.678 and 0.9811-0.9992, respectively. The selectivity order observed was as follows: UO2 2+ > Fe3+ > Pb2+ > Ni2+ > Mg2+. The magnetic polymers selective to Cr(VI) were also synthesized and were leached with HCl to remove the template. The synthesized Cr(VI) magnetic polymers, the optimum pH obtained was 4 for both the magnetic IIP and the corresponding NIP. The amount of the adsorbent which gave the maximum adsorption was determined to be 20 and 65 mg for the magnetic IIP and NIP, respectively. A Cr(VI) concentration which was adsorbed maximally was from 5 mg L-1 which was therefore taken as the optimum. The maximum adsorption capacities for the magnetic polymers were 6.20 and 1.87 mg g-1 for the magnetic IIP and NIP, respectively. The optimum time for the adsorption of the Cr(VI) analyte was determined as 40 minutes. Investigation of the order of selectivity of anions followed the trend: Cr2O7 2- SO4 2- F- NO3- -.

Usamos o método KKR para a obtenção dos níveis de energia e densidades de carga do ferro FCC (fase paramagnética). Observamos que gerando o potencial cristalino a partir de diferentes configurações atômicas, a carga dentro da esfera é a mesma e os níveis de energia também o são a menos de uma constante aditiva. Verificamos também que a carga dentro das esferas circunscrevendo os átomos é linear com o salto V(R) V BARRA IND. II do potencial na superfície das esferas, o que sugere importante simplificação no processo de auto-consistência. / We use the KKR method to obtain the energy bands and the charge of the density of the paramagnetic fcc iron. We observe that self- consistent energy bands can be derived from different atomic configuration as long as the total charge inside the iron spheres is self-consistent. We observe also that the discontinuity of the potential VII V(R) at the spheres is linear with the charge in the spheres. This fact suggest a very simple method to make approximatively self-consistent band calculations.

Usamos o método KKR para a obtenção dos níveis de energia e densidades de carga do ferro FCC (fase paramagnética). Observamos que gerando o potencial cristalino a partir de diferentes configurações atômicas, a carga dentro da esfera é a mesma e os níveis de energia também o são a menos de uma constante aditiva. Verificamos também que a carga dentro das esferas circunscrevendo os átomos é linear com o salto V(R) V BARRA IND. II do potencial na superfície das esferas, o que sugere importante simplificação no processo de auto-consistência. / We use the KKR method to obtain the energy bands and the charge of the density of the paramagnetic fcc iron. We observe that self- consistent energy bands can be derived from different atomic configuration as long as the total charge inside the iron spheres is self-consistent. We observe also that the discontinuity of the potential VII V(R) at the spheres is linear with the charge in the spheres. This fact suggest a very simple method to make approximatively self-consistent band calculations.

No description available.

A new method is proposed to enhance the gain and efficiency of planar printed antennas. The proposed method is based on using artificial magnetic materials as a superstrate for planar printed antennas while maintaining the low-profile attractive feature of these antennas. It is found that the antenna's gain increases as the permeability of the superstrate increases. Due to the lack of low-loss natural magnetic materials in the microwave band, designing artificial materials with magnetic properties has become increasingly attractive in recent years. In particular, using magneto-dielectric superstrates reduces the wavelength in the media leading to a miniaturized composite structure (antenna with superstrate). The split ring resonator SRR is used as a unit cell of an artificial magnetic superstrate for a microstrip antenna to enhance the antenna gain and efficiency. Also, in this work, mechanism of operation for artificial magnetic materials is theoretically investigated. Analytical and numerical methods are provided to model the behaviour of these materials. Full-wave analysis of multilayered periodic structures is an expensive computational task which requires considerable computer resources. In this work, a fast analytical solution for the radiation field of a microstrip antenna loaded with a generalized superstrate is proposed. The proposed solution is based on using the cavity model in conjunction with the reciprocity theorem and the transmission line analogy. The proposed analytical formulation reduces the simulation time by two orders of magnitude in comparison with full-wave analysis. The method presented in this work is verified using both numerical and experimental results for the case of a patch antenna covered with an artificial 3D periodic superstrate. Another useful feature of a microstrip antenna covered with superstrate is controlling the direction and beamwidth of the main beam of the antenna. Beam steering has been traditionally implemented in antenna arrays using phase shifters which result in complex and expensive structures and suffer from high loss and mass. This work provides a novel method to steer the main beam of a patch antenna by partially covering it with a high refractive index superstrate. The beam steering of a single patch is possible because of the dual-slot radiation mechanism of the microstrip antenna (according to the cavity model). Full-wave simulations, analytical modeling and experiments are provided to support the proposed technique of beam steering in planar antennas.