Synthèse chimique, structure et propriétés magnétiques de nanoparticules d'alliage FePt

Michael Delalande 1
1 NM - Nanostructures et Magnétisme
SP2M - UMR 9002 - Service de Physique des Matériaux et Microstructures : DSM/INAC/SP2M
Abstract : FePt nanoparticles are of significant importance because of their potential application in magnetic storage devices beyond Tbit/in2. This work deals with the study of the structural and magnetic properties of chemically synthesised FePt particles. We show that structural and magnetic properties of the as-grown particles indicate a core-shell structure for nanoparticles prepared with various methods : an iron-depleted core (Fe30Pt70) surrounded by a iron-rich shell. Combining structural, magnetic and chemical data, we suggest this structure originates from the difference in the kinetics of incorporation of Pt and Fe, which are mainly controlled by the two ligands (oleic amine and acide). We then investigated a novel combinations of ligands (replacing the amine by pentadecanenitrile), and indeed obtained nanoparticles with a more homogeneous composition. As-synthesised FePt nanoparticles are in the chemically disordered structure and thermal annealing at 650°C is required to obtain the L10 phase. We proved that iron atoms of the shell are available to form of the ordered phase in core-shell nanoparticles. However, thermal annealing of assemblies of nanoparticles results in large sintering. We then started to explore an alternative process relying on irradiation by light ions at moderate temperatures. First results are encouraging as irradiation at 300°C leads to both a more homogeneous composition and a higher magnetisation of the nanoparticles.
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Michael Delalande. Synthèse chimique, structure et propriétés magnétiques de nanoparticules d'alliage FePt. Physique [physics]. Université Joseph-Fourier - Grenoble I, 2007. Français. ⟨tel-00371313⟩

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