Um modelo de excitações interagentes para descrição de gelos de spins artificiais

• Ano de defesa: 2018
• Autor(a) principal: João Henrique Rodrigues
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Monopolos magnéticos; Excitações emergentes; Gelos de spins; Modelo Efetivo; Modelos de spins; Transição de fase; Física computacional; Magnetismo
• Link de acesso: http://hdl.handle.net/1843/SMRA-BBSFX8

Artificial spin ice is a class of two dimensional nanomagnetic systems fabricated by litography. They are initially proposed to resemble the crystalline spin ice, allowing the theoretical and experimental investigation of phenomenona such as geometric frustration, emergent excitations, system dynamics in and out of equilibrium, and so on. In this work, we are interested in studying the emergent excitations of the artificial spin ice, aiming to verify what characteristics they bring to these systems in a magnetization reversal process. To do so, we developed an emergent vertex model based on a dumbbell model. We show that such a model is equivalent to the original spin model, reproducing properly its thermodynamic properties. The model also allows to analyze separately the contributions generated in the system by monopole and dipole excitations. We use this knowledge to alter the contributions coming exclusively from monopole excitations in the artificial square and triangular spin ice and verify how they modify the characteristics of its vertex population curves in a magnetization reversal process. We have found that the monople presence causes both lattice to present the population curves of the central region left asymmetric. This feature appears even when the lattice have high disorder and temperature fluctuations, being better observed when there are low disorders and/or there are thermal fluctuations. We expect these characteristics can be used to directly stipulate the monopole excitations charge in experimental measurements.