Efeitos de campo elétrico cristalino na família de compostos intermetálicos TRNi3Ga9 (TR=Gd, Tb, Dy, Ho, Er, Lu)

• Ano de defesa: 2017
• Autor(a) principal: Silva, Leonardo de Sousa
• Orientador(a): Duque, José Gerivaldo dos Santos
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Sergipe
• Programa de Pós-Graduação: Pós-Graduação em Física
• País: Brasil
• Palavras-chave em Português: Física; Teoria do campo cristalino; Campos elétricos; Compostos intermetálicos; Magnetismo
• Área do conhecimento CNPq: CIENCIAS EXATAS E DA TERRA::FISICA
• Link de acesso: https://ri.ufs.br/handle/riufs/5253

In this work, monocrystalline samples of the system TRNi3Ga9 (TR = Gd Tb, Dy, Ho, Er, Lu) were synthesized by the metal flux technique. The physical properties were studied by X-ray diffraction, magnetic susceptibility, function field magnetization, electrical resistivity and specific heat. This family of compounds crystallizes into a trigonal structure of type ErNi3Al9 with spatial group 32. The LuNi3Ga9, non-magnetic isostructural sample was used to subtract lattice and electronic contributions to the Cp for the other rare earths. In the samples grown with TR = Gd, Tb, Dy, Ho, Er show antiferromagnetic ordering with TN < 20 K. Except for the sample GdNi3Ga9 an anisotropic behavior was observed in the curves of (T) e M(H) as a function of the direction of application of the magnetic field Which we associate with effects of crystalline electric field (CEF). Furthermore, both the TN and the term CW do not stagger with the term of de Gennes indicating that the CEF effects and the anisotropic character of the exchange interaction are present in this family of compounds. In order to analyze the evolution of the magnetic properties along this series of compounds we use a mean field model including anisotropic exchange interactions, crystalline electric field effects and quadrupole interactions. The measures of (T), M(H) and of the specific heat were simulated for emph TR = Tb, Dy, Ho and Er making it possible to extract the exchange parameters (J′s), the terms of CEC (B′s) and the quadrupolar terms (K′s). In addition, from this data set is constructed the levels scheme of the crystalline electric field with its respective wave functions. The analysis of the data extracted from the simulation allows us to understand the change in orientation of the axis of easy magnetization throughout the series. To TR = Tb, Dy easy magnetization axis is located along the ab plane, whereas for the TR = Er, the easy magnetization axis is oriented in the direction c. This behavior is consistent with the signal change in the CEF B0 2 term which was negative for ErNi3Ga9 and positive for the other rare earths. In addition, the total division of the multiplet of the CEF scheme of levels decreases with the increase of the atomic number (Tb - Er) of the rare earth ion in the same way as the dominant term of the CEF Hamiltonian, B0 2 . We have tried to associate this fact with the systematic change in the c/a ratio that increases from Tb to Er.