Estudo do efeito magnetocalórico nos sistemas amorfos Eu80Au20 e TRNi3 (TR = Dy, Ho e Er)

• Autor(a) principal: Costa, Samir Santos
• Data de Publicação: 2016
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UERJ
• Texto Completo: http://www.bdtd.uerj.br/handle/1/12966
• topic: Magnetocaloric effect; Amorphous; Rare earth; Spin hamiltonians; Magnetic properties; Efeito magnetocalórico; Amorfos; Terras-raras; Hamiltonianos de Spin; Propriedades magnéticas; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA::FISICA DA MATERIA CONDENSADA

In this work some magnetic and magnetocaloric properties were investigated in amorphous Eu80Au20 and TRNi3 (TR = Dy, Ho e Er) systems considering that the magnetic matrix of each material consists just by rare-earth ions. The first is dealt from the perspective of Handrich-Kaneyoshi model that, from a hamiltonian which includes the exchange and Zeeman interactions, provides an expression for a temperature dependent reduced magnetization. The others, besides the contributions mentioned, show another interaction type that implies in a local anisotropy and, therefore, are treated by HPZ model. The amorphization and molecular field parameters were obtained for Eu80Au20 system from the magnetization against temperature measurements; a study of the magnetocaloric effect was carried out by analyzing the ∆Siso and ∆Tad potential and refrigerant capacity. As for TRNi3, the anisotropy and molecular field parameters were determined, allowing an analysis of the competitive nature of these; only the ∆Siso potential and capacity refrigerant were determined for these compounds . A discussion about possible applicabilities of such materials on the magnetic refrigeration was made based on the temperature ranges which they show better efficiency for this purpose.