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.

Micromagnetic modeling numerically solves magnetization evolution equation to process magnetic domain analysis, which helps to understand the macroscopic magnetic properties of ferromagnets. To apply this method in simulation of magnetostrictive ferromagnets, there exist two main challenges: the complicated microelasticity due to the magnetostrictive strain, and very expensive computation mainly caused by the calculation of long-range magnetostatic and elastic interactions. A parallel computing for phase field model based on computer cluster is then developed as a promising tool for domain analysis in magnetostrictive ferromagnetic materials. We have successfully built an 8-node Apple workgroup cluster, deploying the hardware system and configuring the software environment, as a platform for parallel computation of phase field model of magnetic materials. Several testing programs have been implemented to evaluate the performance of the cluster system, especially for the application of parallel computation using MPI. The results show the cluster system can simultaneously support up to 32 processes for MPI program with high performance of interprocess communication. The parallel computations of phase field model of magnetic materials implemented by a MPI program have been performed on the developed cluster system. The simulated results of a single domain rotation in Terfenol-D crystals agree well with the theoretical prediction. A further simulation including magnetic and elastic interaction among multiple domains shows that we need take into account the interaction effects in order to accurately characterize the magnetization processes in Terfenol-D. These simulation examples suggest that the paralleling computation of the phase field model of magnetic materials based on a powerful cluster system is a promising technology that meets the need of domain analysis.

Thesis (Ph.D.)--University of Wollongong, 2009. / Typescript. Includes bibliographical references: leaf 174-191.

Thesis (Ph. D.)--School of Chemistry and Biochemistry, Georgia Institute of Technology, 2004. Directed by Z. John Zhang. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--Florida State University, 2003. / Advisor: Dr. Elbio Dagatto, Florida State University, Dept. of Physics. Title and description from dissertation home page (Nov. 21, 2003). Includes bibliographical references.

This dissertation explores magnetic-field- and electric-current-driven domain-wall motion in thin-film-based magnetic microstructures. Conventional thin-film growth and microstructure fabrication techniques including electron-beam lithography and focused ion beam milling are used to fabricate nanometer-scale one-dimensional and two-dimensional magnetic structures that support magnetic domains (regions of different magnetization orientation separated by domain walls). A high-spatial resolution, hightemporal resolution technique for measuring the field- or current- driven dynamics of the domain walls, based on the magneto-optic Kerr effect, is developed and used to study the wall dynamics. Field-driven domain-wall motion at slow magnetic field sweep rates is dominated by Barkhausen jumps, the discontinuous random movement of domain-wall displacements. The experiments described represent one of the first successful attempts to extend the study of Barkhausen effects into the two-dimensional region. The experiments successfully probe velocity distributions, jump amplitude distributions, and attempt to address issues that pertain to the universal exponents that describe the scaling behavior of Barkhausen jump distribution function including effects of dimensionality and sweep-rate effects on the exponents. A novel dual-beam magneto-optical experiment is performed on thin-film microstructure that probes negative Barkhausen jumps (jumps that oppose the direction favored by Zeeman energy driving the magnetic reversal). A new mechanism for negative Barkhausen jumps is proposed that accounts for the observed effects. Domain-wall motion driven by (spin-polarized) electric current is studied in nanoscale thin-film based wires. The experiments address issues pertaining to the basic mechanisms responsible for current-driven domain-wall motion, which are believed to be the adiabatic spin-torque mechanism and non-adiabatic mechanisms. The experiments described are the first true time-resolved measurements of current-driven displacements, and the results reveal new information about the stochastic properties of current-driven domain wall displacements. The results also provide information on domain-wall velocities and spin-flip efficiencies that address issues related to spin-torque mechanisms.

No description available.