Estudo da reorientação de spin nos compostos RX2 (R = terra rara; X: Al, Ni)

• Autor(a) principal: Souza, Marcos Vinicios de
• Data de Publicação: 2013
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da UFS
• Texto Completo: https://ri.ufs.br/handle/riufs/5290
• topic: Reorientação de spin; Terras raras; Campo cristalino; Anisotropia; Magnetismo; Materiais magnéticos; Teoria do campo cristalino; Correntes elétricas; Eletrostática; Terras-raras; Troca de Spin; Particulas de spin; Reorientation of spin; Rare Earths; Crystalline Field; Anisotropy; Crystal field theory; Earths, Rare; Electric currents; Electrostatics; Magnetic materials; Magnetism; Spin exchange; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA

In this work, our initial efforts have been directed to study the behavior of the magnetization as a function of temperature, calculated according to the approximate method of the anisotropy constants and the resolution of a Hamiltonian (that includes the crystal field) as exemplified for the DyAl2 compound. Furthermore, we investigated the magneto-thermal characteristics of some members of the RX2 series (R: rare earth, X: Al, Ni), including spin reorientation (SR), by using a model Hamiltonian, that consists of localized magnetic moments interacting via exchange and crystal field interaction, in the molecular-field approximation. We studied how the SR depends on the direction of the application of magnetic field, the intensity of this field and temperature. For the magnetic calculations, the problem of self-consistency was solved by using a computational routine developed in the Fortran 90 programming language. We emphasize that special attention was directed to the crystal field, because of its high relevance to the anisotropic characteristics of the RX2 studied compounds. Thus, in our attempts to study the peculiarities of the rare earth elements, due to crystal field effects, we have not only considered the intensity change, but the direction change of the applied field. In the cases of both Er+3 and Tb+3 compounds, we obtained second-order or continuous magnetization behavior along the polar angle axis. We stressed that the crystal field terms plays an important role in the first order spin reorientation for Dy+3 and Ho+3 compounds. First, it can be revealed by the discontinuity in the Cartesian components of the magnetization vector as a function of the polar angle. Second, the discontinuity is of great importance in the calculation of latent heat associated to the spin reorientation in the case where the first order transitions were observed. Finally, we were able to separate the first and second order contributions of the anisotropic magnetic entropy change, which is the main result of this work.