Estudo do efeito magnetocalórico em sistemas magnéticos com terras raras

• Autor(a) principal: Sousa, Vinícius da Silva Ramos de
• Data de Publicação: 2010
• 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/1/12827
• topic: Magnetocaloric effect; Anisotropic magnetocaloric effect; Intermetallics; Rare earth; Crystal field; Spin reorientation; Ferrimagnetism; Efeito magnetocalórico; Efeito magnetocalórico anisotrópico; Intermetálicos; Terras raras; Campo cristalino; Reorientação de spin; Ferrimagnetismo; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA::FISICA DA MATERIA CONDENSADA

The magnetic refrigeration is based on the magnetocaloric effect. The magnetocaloric potential is characterized by the two thermodynamics quantities: the isothermal entropy change (ΔSiso) and the adiabatic temperature change (ΔTad), which are calculated upon a change in the intensity of the applied magnetic field. In anisotropic magnetic systems it is observed a change in the magnetocaloric effect, since this potential becomes strongly dependent on the direction in which the external magnetic field is applied. The anisotropy in such magnetic systems can lead to an inverse magnetocaloric effect, as well as to the definition of an anisotropic magnetocaloric effect, that by definition is calculated upon a magnetic field which intensity is kept fixed and which orientation is changed from a hard direction of magnetization to the easy direction of magnetization. This anisotropic magnetocaloric effect was performed for the RAl2 intermetallic compounds considering a microscopic model Hamiltonian that includes the Zeeman interaction, the exchange interaction (taken in the mean field approximation) and the crystalline electrical field, that is responsible for the anisotropy in the RAl2 compounds. The anisotropic magnetocaloric was fully investigated for the serie RAl2 and compared with the usual magnetocaloric effect and several curves of (ΔSiso) and (ΔTad) were obtained.