On the synthesis and magnetocaloric effect of Fe2P, Mn2Sb and MnAs based compounds / Da sintese e do efeito magnetocalorico de compostos derivados do Fe2P, Mn2Sb e MnAs

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

On this PhD thesis some results on the magnetic, magnetocaloric and structural properties of some series of compounds suitable for applications on magnetocaloric effect-based refrigeration are presented. The FeMnP1-xAsx series preparation methods are studied in order to optimize their magnetocaloric properties as well as to shorten its preparation time. A new series of compounds based on the previous one was studied, the MnFeGe1-xSix. These compounds present a second-order magnetic phase transition and a linear change in lattice parameters with Si content on the 0 £ x £ 0.7 range. Also associated with a second-order phase transition, the magnetocaloric effect on FeMnSn was discovered around room-temperature. A careful study of Mn2Sb-based compounds with Mn partially substituted by Cr, V, Co and Cu and Sb by Ge was performed. On these compounds an Exchange Inversion transition is induced by substitutions taking the material from the ferrimagnetic to the antiferromagnetic state with decreasing temperature, giving rise to the so-called inverse magnetocaloric effect. A phenomenological theoretical model was also developed to describe such transitions and their associated magnetocaloric effect. Finally we report on the colossal magnetocaloric effect on Cu-substituted MnAs compounds. Due to this compound?s unusual behavior, the magnetic measurements of the magnetocaloric effect are reviewed. Based on the results of different measurement procedures a new method of measurement for highly hysteretic compounds is proposed which leads to non spurious results

ASSUNTO(S)

transition-metal compounds efeito magnetocalorico refrigeração magnetica magnetocaloric effect magnetic refrigeration materiais baseados em metais de transição

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