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Multiferroic oxide-based thin films applied to magnetic refrigeration

Abstract : Energy is essential for humans in everyday life and critical to economic growth and developement progress in industrial sectors. The global energy sources are mostly from fossil resources (e.g oil, coals, gas) being dominant source of local air pollution and emitter of the most dangerous green house gases such as carbon dioxide (CO2), largely responsible for the ozone layer depletion. In the context of the current shortage of those ressources due to the continuously increase in demands in energy and while fossil reserves will eventually run out, the discovery and development of a low-carbon technologies become critical with the need to decarbonise and reduce our dependency to fossil fuels. One of theses technologies is the magnetic refrigeration based on the magnetocaloric effect (MCE). In this thesis, we have investigated the magnetic and magnetocaloric properties of strongly correlated oxides thin films grown by pulsed laser deposition in view of their portential application in magnetic cooling. The obtained results reveal that the magnetic and magnetocaloric properties of PrVO3 (PVO) compounds can be easy tailored by using the thin films approach. Particularly, the coercive magnetic field was dramatically decreased making from the PVO compound a nearly soft magnet in the region where the magnetic entropy change is released as well as a considerable increase in saturation magnetization. Accordingly, a giant magnetocaloric effect is exhibited by PVO thin films grown on LSAT substrate at low temperatures showing the great impact of strain effects. This finding opens the way for the implementations of PVO thin films in some specific applications such as on-chip magnetic cooling of a nanoelectronic device and sensor technology. On the other hand, the DFT calculations have confirmed the ground state and the competition between magnetic interactions under compressive strains in PVO thin films. Our result not only suggests that epitaxial PVO thin films is potential for refrigeration at cryogenic temperatures but may also pave the way to create many novel functionalities in perovskite-type transition metal oxides by control of structural aspects.The mechanisms leading to the giant anisotropic magnetocaloric effect observed in HoMn2O5 single crystals are also studied. Both DFT calculations and Monte Carlo simulation allowed us to explore the role of Holmium ions as the main contributor to the MCE as well as the of the importance of the intrinsic anisotropic properties as a promising way to optimize the MCE for magnetic refrigeration application at low temperature regime as well as the implementation of compact and efficient rotary magnetic refrigerators.
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Submitted on : Thursday, January 21, 2021 - 4:13:23 PM
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  • HAL Id : tel-03117868, version 1

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Hamza Bouhani. Multiferroic oxide-based thin films applied to magnetic refrigeration. Physics [physics]. Université de Lorraine; Université Mohammed V (Rabat), 2020. English. ⟨NNT : 2020LORR0131⟩. ⟨tel-03117868⟩

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