Ludwigita, homometálica de cobalto : síntese, magnetismo e estrutura cristalina

• Autor(a) principal: Freitas, Daniele Cristina Silva de
• Data de Publicação: 2009
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Federal Fluminense (RIUFF)
• Texto Completo: https://app.uff.br/riuff/handle/1/17278
• topic: Espectroscopia de ressonância magnética; Magnetic resonance spectroscopy; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA

This work presents the synthesis method, single crystal X-ray diffraction measurements at different temperatures and some magnetic properties of the cobalt ludwigite Co3O2BO3. The results were compared with those obtained for iron ludwigite Fe3O2BO3 whose structure is isomorph (space group Pbam in ambient temperature). We could verify that the cobalt ions charge in diferents sites of the lattice are near those of the iron ions in the corresponding sites. As well it was veriffed that the two ludwigites exhibit a transition from a paramagnetic phase to a antiferromagnetic phase presenting weak ferromagnetism. A genuine ferromagnetic phase below 10 K, absent in the iron ludwigite, has been observed. Also, the magnetic irreversibility curve has been studied. The structural phase transition exhibited by iron ludwigite was not clearly observed in the cobalt ludwigite. Another important property observed in the iron ludwigite is the coexistence of paramagnetism and magnetic ordering. We also could not characterize this phenomenon without ambiguity in the cobalt ludwigite because we had no condition of realizing especiffic heat measurements with small quantities of sample. Only accidents in the a.c. susceptibility curves suggest a second magnetic transition in the material. Based in Vallejo and Avignon theory we believe that the structural transition in the iron ludwigite is much more visible that in cobalt ludwigite because the magnetic energy in this ludwigite is smaller that in the iron ludwigite.