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Theses

Différents matériaux à effet magnétocalorique : Aspects fondamentaux et applicatifs

Abstract : This thesis reports on the study of several materials -mainly oxides- with the aim of applications in magnetic refrigeration (MR). Four main aspects were addressed: (1) Research of materials with high magnetocaloric effect (MCE), (2) MCE physics and its experimental characterizations, (3) production of material for direct tests in a MR device at room temperature, and (4) additional studies beyond the scope of MR. (1) The A-site ordering in manganites (R1-xAExMnO3) or their incorporation in super-lattices were found to be new ways to adjust the MCE around room temperature. As an example of a first-order transition (FOT), we investigated the case of Eu0.58Sr0.42MnO3 which led to an intense MCE, as expected. Significant MCEs were also measured around the second-order ferrimagnetic transition in Mn3O4, and around a spin and valence states transition in Pr0.49Sm0.21Ca0.3CoO3. The existence of giant MCE was confirmed in the Heusler alloy Ni45Co5Mn37.5In12.5 by heat capacity measurements. (2) Some controversies about the MCE determination by magnetic and calorimetric methods were addressed in detail. Special attention was paid to the case of FOTs when they exhibit phenomena such as phase separation and/or magneto-thermal history. (3) Two systems (La1-xKxMnO3 and Pr1-xSrxMnO3) were investigated for applications at room temperature. Preliminary results are reported on a regenerator constituted of Pr0.65Sr0.35MnO3 plates. (4) Peculiar phenomena encountered in Mn3O4 (a new transition below TC), in Pr0.49Sm0.21Ca0.3CoO3 (a coupling between valence and spin states transitions) or Eu0.58Sr0.42MnO3 (spin-glass state) were the subject of dedicated studies.
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Submitted on : Tuesday, December 6, 2011 - 11:44:41 AM
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  • HAL Id : tel-00648672, version 1

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Francois Guillou. Différents matériaux à effet magnétocalorique : Aspects fondamentaux et applicatifs. Science des matériaux [cond-mat.mtrl-sci]. Université de Caen, 2011. Français. ⟨tel-00648672⟩

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