O efeito magnetocalórico nos compostos (La,TR)[Fe0,88Si0,12]13, onde TR=Y ou Gd

• Autor(a) principal: Demuner, Aline da Silva
• Data de Publicação: 2008
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Federal do Espírito Santo (riUfes)
• Texto Completo: http://repositorio.ufes.br/handle/10/4760
• topic: Refrigeration; Magnetic Materials; Refrigeração; Materiais magnéticos; Física; Refrigeração; Materiais magnéticos; 53

In this work, the Magnetocaloric Effect (EMC) (for quantification of the magnetic entropy variation (?SM)) in the compounds La(1-x)(RE)x[Fe0.88Si0.12]13, with 0.05 = x = 0.20, was experimentally verified by partial substitution of the La atoms by Y or Gd atoms (RE). The obtained samples were characterized by X-ray diffraction (XRD), Mössbauer Spectroscopy and magnetization measurements as a function of the temperature and of the magnetic field. The latter ones allowed the calculation of the EMC, which was evaluated as a function of the concentration x of Y or Gd. The XRD results in the Y – based compounds indicate that the samples stabilize in the NaZn13-type structure, however, accompanied by the formation of other Fe - rich phases (a-(Fe,Si) e LaFeSi). The magnetization measurements as a function of the temperature under low magnetic field (0.05T) show that, through the whole compositional interval (0.05 = x = 0.20), the compounds present a magnetic transition (Ferromagnetic ? Paramagnetic) at a temperature, TC, below room temperature. On the other hand, it was observed in the magnetization measurements as a function of the applied magnetic field, that for certain concentrations of Y or Gd (x= 0.05 (Y); x= 0.05 e 0.20 (Gd)), the curves start to present a characteristic behavior of a field induced metamagnetic transition. In the series La(1-x)Yx[Fe0.88Si0.12]13, the maximum value of the ?SM found, for a field of 5T, was -20.2 J/kg.K corresponding to an temperature interval T = 18.3 K, for the sample with x=0.05. As for the series La(1-x)Gdx[Fe0.88Si0.12]13, the found value was ?SM = -21.0 J/kg.K corresponding to an temperature interval T = 19.1 K, for the sample with x=0.20. These results (?SM) are attributed to the field induced metamagnetic transition, as observed in the Arrot plots (M2 in function of H/M)