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Synthèses chimiques, transformation de phase et étude des propriétés magnétiques des nanoparticules de FePt et FePd

Abstract : This work aims at understanding the chemical synthesis of FePt and FePd nanoparticles (NPs), and at exploring how to implement the phase transformation from the chemically disordered to the L10 phase, without coalescence. Using hexadecanenitril instead of oleylamine, we obtain NPs with a more homogenous internal composition, instead of core-shell NPs. Through a systematic study (designed experiment relying on Taguchi tables), we developed the FePd synthesis, while evidencing the role of each ligand and of the reductor. To induce the crystalline phase transformation while avoiding coalescence, we explored two ways. In the first one, atomic vacancies are introduced in the NPs through light ion irradiation, atomic mobility being ensured by annealing at moderate temperature (300°C). As a result, the blocking temperature is multiplied by 4, due to anisotropy enhancement. However, strong chemical ordering in the L10 phase cannot be achieved. The second approach relies on the dispersion of the NPs in a salt (NaCl) matrix, prior to annealing at 700°C: high chemical ordering is achieved, and the blocking temperature is beyond 400°C. We then developed a single-step process to remove the salt by dissolution in water and to re-disperse NPs in stable aqueous or organics solutions. These high magnetic anisotropy NPs are then readily available for further chemical or manipulation steps, with applied perspectives in areas such as data storage, or biology.
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Submitted on : Monday, February 28, 2011 - 4:40:52 PM
Last modification on : Wednesday, November 4, 2020 - 2:48:51 PM
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Anastasia Delattre. Synthèses chimiques, transformation de phase et étude des propriétés magnétiques des nanoparticules de FePt et FePd. Matériaux. Université Joseph-Fourier - Grenoble I, 2010. Français. ⟨tel-00570569⟩

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