Estudo das propriedades térmicas e magnéticas nos compostos Gd1-xTbxAl2, Er1-xTbxAl2, e TbS b

• Autor(a) principal: Ribeiro, Paula de Oliveira
• Data de Publicação: 2016
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UERJ
• Texto Completo: http://www.bdtd.uerj.br/handle/1/12874
• topic: Magnetocaloric effect; Crystalline eletrical field; Resistivity; Magnetoresistivity; Efeito magnetocalórico; Campo elétrico cristalino; Resistividade; Magnetoresistividade; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA::FISICA DA MATERIA CONDENSADA

In this thesis we studied the thermal and magnetic properties focusing on the magnetocaloric effect (MCE) of the Gd - Tb - Al2, Er - Tb - Al2 and TbS b compounds. In order to do this, we considered a model hamiltonian which take into account a magnetic lattice formed by coupled sublattices. We included the Zeeman interaction, crystalline electrical field and exchange interaction in the Hamiltonian. Firstly, we discussed the main aspects of the basics models for the interested magnetic and electric systems. We also discussed the main aspects of the mean field approximation coupling the two magnetic sublattices model. The thermodynamics properties involved on the magnetocaloric effect and also on the magnetoresistivity, were discussed. Lastly, we showed the results for ours interested compounds. For the Gd1-xTbxAl2 it can be highlight the systematic study of the Curie temperature as a function of applied pressure.We developed a methodology with which it was possible to reproduce the experimental data, and also estimate the pressure effect on the Gd0:6Tb0:4Al2 compound. For the series Er1-xTbxAl2,the temperature and magnetic field dependence of the magnetization alignment processes along the main crystallographic directions were investigated. The MCE considering the applied magnetic field variation along the easy and non easy directions were calculated, Good agreement between the experimental data and calculation for the easy direction were obtained. For the antiferromagnetic TbS b compound, we also studied the MCE. The intensity and direction of the magnetic field dependence on the resistivity were calculated. The magnetoresistivity effect was also calculated.