Propiedades dinámicas y termodinámicas de modelos magnéticos con interacciones competitivas /

Tesis (Doctor en Física)--Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física, 2009.En esta tesis se estudian propiedades termidinámicas y dinámicas mediante simulaciones de Monte Carlo de dos modelos magnéticos con interacciones competitivas, con variables de espín clásicas. En el primer caso, el modelo consiste en una red cúbica de espines con interacciones competitivas de corto alcance, entre primeros y segundo vecionos. Se estudia el diagrama de fases, metaestabilidades, y la dinámica de relajación a dos tiempos. En el segundo caso se estudian propiedades termodinámicas de un modelo de películas magnéticas ultradelgadas, con interacciones competitivas de corto y largo alcance. Se confecciona el diagrama de fases a campo nulo, y se obtienen resultados sobre la transición de reorientación de espines.Marianela Carubelli

Inverse transition in the two dimensional dipolar frustrated ferromagnet

We show that the mean field phase diagram of the dipolar frustrated ferromagnet in an external field presents an inverse transition in the field-temperature plane. The presence of this type of transition has recently been observed experimentally in ultrathin films of Fe/Cu(001). We study a coarse-grained model Hamiltonian in two dimensions. The model supports stripe and bubble equilibrium phases, as well as the paramagnetic phase. At variance with common expectations, already in a single mode approximation, the model shows a sequence of paramagnetic-bubbles-stripes-paramagnetic phase transitions upon lowering the temperature at fixed external field. Going beyond the single mode approximation leads to the shrinking of the bubbles phase, which is restricted to a small region near the zero field critical temperature. Monte Carlo simulations results with a Heisenberg model are consistent with the mean field results.Comment: 8 pages, 6 figure

Inverse transition in a two-dimensional dipolar frustrated ferromagnet

We show that the mean-field phase diagram of the dipolar frustrated ferromagnet in an external field presents an inverse transition in the field-temperature plane. The presence of this type of transition has recently been observed experimentally in ultrathin films of Fe/Cu(001). We study a coarse-grained model Hamiltonian in two dimensions. The model supports stripe and bubble equilibrium phases, as well as the uniform phase. At variance with common expectations, already in a single-mode approximation, the model shows a sequence of uniform-bubbles-stripes-uniform phase transitions upon lowering the temperature at a fixed external field. Going beyond the single-mode approximation leads to the shrinking of the bubbles phase, which is restricted to a small region near the zero-field critical temperature. Monte Carlo simulations results with a Heisenberg model are consistent with the mean-field results

Guías de trabajos prácticos de laboratorio en formato de infografía

Fil: Bárcena, Carlos. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Física; Argentina.Fil: Carubelli, Marianela. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Física; Argentina.Fil: Menendez, Pablo. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Física; Argentina.Fil: Módena, Hugo. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Física; Argentina.En este trabajo se busca dar una nueva visión, o giro al formato de presentación de las guías de trabajo práctico de laboratorio. Los motivos para esto están relacionados en dirigir los esfuerzos en la mejora de la enseñanza de la Física. Teniendo en cuenta la forma en que los estudiantes acceden a la información y la popularidad que los medios de comunicación han alcanzado, es que se propone presentar las guías de trabajos prácticos, aprovechando los recursos tecnológicos tales como la PC y tablet.Fil: Bárcena, Carlos. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Física; Argentina.Fil: Carubelli, Marianela. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Física; Argentina.Fil: Menendez, Pablo. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Física; Argentina.Fil: Módena, Hugo. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Física; Argentina.Otras Ciencias Física

Spin reorientation transition and phase diagram of ultrathin ferromagnetic films

We show results from Monte Carlo simulations of a two-dimensional Heisenberg model for ultrathin films with perpendicular anisotropy. A complete phase diagram is obtained as a function of anisotropy and temperature, spanning a wide range of behavior. We discuss our results in relation to experimental findings in different ultrathin films. We observe and characterize a line of spin reorientation transitions. This transition from out-of-plane stripe order to in-plane ferromagnetic order presents an intermediate paramagnetic gap in a finite region of parameter space, as reported in experiments. For large anisotropies, direct transitions from a low temperature stripe phase to a paramagnetic or tetragonal phase with dominant perpendicular magnetization is observed, which is also in agreement with experiments. We also show the phase diagram for a system without exchange, i.e., with pure dipolar and anisotropy interactions. It shows a similar behavior to the ferromagnetic case with antiferromagnetic instead of stripe phases at low temperatures. A spin reorientation transition is also found in this case

Inverse transition in a two-dimensional dipolar frustrated ferromagnet

We show that the mean-field phase diagram of the dipolar frustrated ferromagnet in an external field presents an inverse transition in the field-temperature plane. The presence of this type of transition has recently been observed experimentally in ultrathin films of Fe/Cu(001). We study a coarse-grained model Hamiltonian in two dimensions. The model supports stripe and bubble equilibrium phases, as well as the uniform phase. At variance with common expectations, already in a single-mode approximation, the model shows a sequence of uniform-bubbles-stripes-uniform phase transitions upon lowering the temperature at a fixed external field. Going beyond the single-mode approximation leads to the shrinking of the bubbles phase, which is restricted to a small region near the zero-field critical temperature. Monte Carlo simulations results with a Heisenberg model are consistent with the mean-field results

Spin reorientation transition and phase diagram of ultrathin ferromagnetic films

We show results from Monte Carlo simulations of a two-dimensional Heisenberg model for ultrathin films with perpendicular anisotropy. A complete phase diagram is obtained as a function of anisotropy and temperature, spanning a wide range of behavior. We discuss our results in relation to experimental findings in different ultrathin films. We observe and characterize a line of spin reorientation transitions. This transition from out-of-plane stripe order to in-plane ferromagnetic order presents an intermediate paramagnetic gap in a finite region of parameter space, as reported in experiments. For large anisotropies, direct transitions from a low temperature stripe phase to a paramagnetic or tetragonal phase with dominant perpendicular magnetization is observed, which is also in agreement with experiments. We also show the phase diagram for a system without exchange, i.e., with pure dipolar and anisotropy interactions. It shows a similar behavior to the ferromagnetic case with antiferromagnetic instead of stripe phases at low temperatures. A spin reorientation transition is also found in this case