Ferromagnetismo diluído de semicondutores mistos CeO2-ZnO:M (M = Fe, Co, Ni)

• Ano de defesa: 2012
• Autor(a) principal: Santos, Tâmara Sibele dos
• Orientador(a): Macêdo, Marcelo Andrade
• 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: BR
• Palavras-chave em Português: Magnetismo; Difratometria; Espectroscopia
• Palavras-chave em Inglês: Magnetism; Spectroscopy; Diffraction
• Área do conhecimento CNPq: CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA
• Link de acesso: https://ri.ufs.br/handle/riufs/5238

In this paper we study the structural and magnetic characterization of samples CeO2, CeO2-Zn and ZnO: M (Fe, Co, Ni) obtained via the proteic sol-gel process, where the organic precursor is coconut water. The solutions were prepared by dissolving cerium nitrate and nitrate zinc for samples doped with Zn and cerium nitrate, zinc and cobalt or iron in the samples doped with Fe or Co and were later brought the muffle where they remained for 24 h at 100 º C to form the xerogel. Then the samples were calcined at 400, 600, 800 and 1000 º C for one hour in air. After calcinations the powders were analyzed in the X-ray diffraction to identify the phases formed and to infer a limit of solubility for the systems studied. By measuring the Raman spectroscopy identified the presence of oxygen vacancies according to the literature to induce a ferromagnetic behavior, in addition to confirming the results obtained using XRD. The magnetic properties were also studied by SQUID magnetometer. In general, the samples studied here showed a ferromagnetic behavior at 2 K with very low values of Hc and Mr and had a saturation magnetization (Ms) increases with increasing concentration of dopant ions and calcinations temperature. It was observed a weak ferromagnetism at room temperature too. Our results indicate that the origin of ferromagnetism is associated with formation of oxygen vacancies. Samples of mixed matrix doped iron showed an interesting change in behavior. When the concentration of dopant ions was x ≤ 0.04 the samples were ferromagnetic when the concentration was x ≥ 0.05 it showed antiferromagnetic with Néel temperature approximately equal to 12, 27 and 13 K for Fe with x = 0.05, 0.075 and 0.1, respectively.