Propriedades magnéticas do modelo de Heisenberg nas aproximações de campo médio e efetivo

• Autor(a) principal: Santos Filho, Adelino dos
• Data de Publicação: 2016
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da UFS
• Texto Completo: https://ri.ufs.br/handle/riufs/5270
• topic: Física; Magnetismo; Anisotropia; Termodinâmica; Mecânica estatística; Diagrama de fase; Termo anisotropia; Função de distribuição; Modelo de Heisenberg; Magnetism; Phase diagram; Term anisotropy; Distribution function; Heisenberg model; CIENCIAS EXATAS E DA TERRA::FISICA

The magnetic properties of materials are primarily dictated by its ion ordering which occurs by means of electrostatic exchange interaction. Many other factors are also involved such as the lattice geometry, non-magnetic ions, anisotropy, external fields, and so forth. In this work, we investigate the ferromagnetic spin 1=2 Heisenberg model within the mean field approximation as well as in the effective field framework in two distinct structures, namely, the kagome and simple cubic lattices. For the kagome structure, we applied the mean field approximation including Dzyaloshinkii-Moriya (DM) anisotropy and an external field. Then, we worked out its phase diagram on the temperature-interaction manifold and analyzed some fundamental thermodynamics properties such as magnetization and magnetic susceptibility for varying (exchange interaction parameter), anisotropy (DM), and temperature. For the simple cubic lattice, we rely on the effective-field approximation by means of the differential operator technique. In this case, we assumed the external field to follow a trimodal distribution and also added a term that accounts for the bond distribution. We then explored the resulting behavior of the phase diagrams. Our findings provide an accurate description of the magnetic behavior of real systems featuring anisotropy and similar topologies.