Integração numérica de equações diferenciais e sua aplicação em dinâmica molecular

-Dinâmica Molecular (MD) é uma das técnicas mais utilizadas em simulações na área de Física. Consiste em resolver equações diferenciais de segunda ordem para obter as posições e velocidades das partículas. O objetivo principal desse trabalho é estudar técnicas de integração aplicadas na solução de equações diferenciais e de desenvolver programas em Fortran 77 para realizar DM de sistemas simples

Monte Carlo study of the critical temperature for the planar rotator model with nonmagnetic impurities

We performed Monte Carlo simulations to calculate the Berezinskii-Kosterlitz-Thouless (BKT) temperature $T_{BKT}$ for the two-dimensional planar rotator model in the presence of nonmagnetic impurity concentration $(\rho)$. As expected, our calculation shows that the BKT temperature decreases as the spin vacancies increase. There is a critical dilution $\rho_c \approx 0.3$ at which $T_{BKT} =0$. The effective interaction between a vortex-antivortex pair and a static nonmagnetic impurity is studied analytically. A simple phenomenological argument based on the pair-impurity interaction is proposed to justify the simulations.Comment: 5 pages, 5 figures, Revetex fil

Método de Monte Carlo aplicado a sistema vítreos dopados com íons terras raras

-O objetivo deste projeto é utilizar métodos numéricos, especificamente o método de Monte Carlo, em sistemas vítreos dopados com íons terras raras. O interesse principal reside na determinação das propriedades ópticas de emissão espontânea (luminescência) e processos não radiativos de transferência de energia. Estes últimos surgem devido à interação eletrostática entre os íons. Pretende-se desenvolver um modelo microscópico que descreva as interações entre íons, particularmente a ordem de interação relevante (ultilizando a expansão em multipolos elétricos) e a formação de clusters. Tais efeitos são de fundamental importância para a caracterização das propriedades destes materiais como meios ativos para laseres, uma vez que os processos de transferência de energia afetam diretamente a eficiência de bombeio. Além disso, o projeto prevê a comparação com dados experimentais a serem obtidos no laboratório de óptica da UFJF

Quantitative behavior study of velocity, radius and topological charge on skyrmion/edge interaction dynamics on Co/Pt nanotrack

Skyrmions are considered promising candidates to be the information carriers in the next generation of data storage and logic devices, due to its stability and easy control under the application of an electric current. For future technological applications in spintronic devices, it is important to study the properties behavior of these topological excitations during its movement on magnetic nanotracks, specially because in ferromagnetic materials they suffer a kind of magnus effect which tends to spell the skyrmion through the borders, preventing its transport throughout the nanotrack. We used micromagnetic simulations to study the dynamics of a skyrmion on a magnetic nanotrack induced by a spin polarized electric current. We considered thin magnetic nanotrack made of cobalt and platinum multilayers, whose magnetic state is perpendicular to the track plane and contain a single Néel-type Skyrmion. To describe this magnetic system, we used a Hamiltonian containing exchange, Dzyaloshinskii-Moriya, perpendicular magnetic anisotropy and dipole-dipole interactions. In our study we observed the well-known Skyrmion Hall effect and changes in the structure of the skyrmion when it approaches of the border. This alteration can be measured by determining the radius and the topological charge of the Skyrmion. Our simulation results show that both the radius and the topological charge decrease when it approaches of the border. Our study also demonstrates that the skyrmion-border interaction is repulsive, but there is a minimum distance from the border at which the interaction becomes attractive. If the skyrmion exceeds this critical position yc, it will be attracted and annihilated at the border of the nanotrack. We also performed simulations to obtain the limit value jc of the applied current density that the skyrmion can be transported along of the nanotrack without escaping from the side edge. From a technological point of view for possible applications in spintronic devices, the estimate of  jc  is of crucial importance