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Study of the LaFe13-xSix(H,C)y and Y1-xRxFe2D4.2 (R = Er, Tb) type compounds for the room temperature magnetic refrigeration.

Etude de composés de type LaFe13-xSix(H,C)y et Y1-xRxFe2D4,2 (R = Er, Tb) pour la réfrigération magnétique à température ambiante.

Author(s) : PHEJAR M.

Type of monograph: Doctoral thesis

Summary

PhD thesis presented at the University Paris-Est Créteil.
The first part of this work was devoted to the elaboration of the LaFe13-xSix (1.2 < x < 2.3) alloys using a synthesis method which had not been applied to these compounds until now : the high energy ballmilling. The synthesis and annealing conditions were defined in order to obtain single phase samples. Their homogeneity was checked by X ray diffraction and electron microprobe analysis. The results show that a finer microstructure is convenient for the formation of the NaZn13 phase and that only a 30 minutes heat treatment at 1373 K is suffcient to obtain almost single phase LaFe13-xSix compounds. This means that this way of synthesis is cost-effective, and thus interesting for industrial production. According to the magnetic measurements, the annealed ball-milled compounds show similar magnetic and magnetocaloric properties than the bulk ones. They exhibit an itinerant electron metamagnetic transition induced by a magnetic field or a temperature change. Their Curie temperatures increase with the Si content from 200 to 235 K when x = 1.4 and 2.0 respectively, while their magnetic entropy variation decreases from 20 to 4 J/kg K under a magnetic field change of 0-2 T. The second part of this study consisted to improve the magnetocaloric properties of the intermetallic compounds by the insertion of light elements such as hydrogen or carbon. According to the literature, the magnetic measurements show a clear increase of the transition temperature until room temperature in both cases. Moreover, the giant magnetocaloric eect is maintained. The evolution of the crystallographic data and the magnetic moment by Fe atom were analyzed by neutron powder diffraction in temperature. This work brings out how interesting are those compounds for their application in room temperature magnetic refrigeration devices. In the framework of new magnetocaloric systems investigation, the magnetic and magnetocaloric properties of the Y1-xRxFe2D4:2 (R = Er et Tb) compounds were studied. Neutron powder diffraction measurements versus field and temperature were performed in complement to magnetic measurements. The large influence of the nature and rate of substituted rare earth has been evidenced.

Details

  • Original title: Etude de composés de type LaFe13-xSix(H,C)y et Y1-xRxFe2D4,2 (R = Er, Tb) pour la réfrigération magnétique à température ambiante.
  • Record ID : 30003845
  • Languages: French
  • Publication: Université Paris-Est Créteil - France/France
  • Publication date: 2011/06/16

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