Source: http://michem.sorbonne-universites.fr/recherche/projets-de-recherche/nanochimie-et-nanotechnologies/post-doctorat-de-yoann-prado.html
Timestamp: 2019-04-23 06:28:03+00:00

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Owing to their magnetic properties, iron oxide nanoparticles are of considerable interest for applications in high-density data storage or in medicine.[1–3] In the case of small particles though, the superparamagnetic limit is reached and the relevant magnetic properties lost. Retaining appealing magnetic properties while maintaining a small nanoparticle size has thus proved a highly challenging task. However, in these small nanoparticles, the magnetic properties are predominantly governed by the surface magnetic anisotropy and modifying it represents one of the best approaches to improve the properties. Following this approach, we have been investigating a novel synthetic strategy to enhance the anisotropy of sub-10 nm maghemite nanoparticles. Surface functionalization was achieved to coordinate anisotropic cobalt containing complexes to the surface of maghemite nanoparticles.
To further our comprehension of the surface anisotropy effect, we have investigated different particles sizes and different complexes (either changing the metal nature (Co, Ni) or the complex geometry). Thus, three batches of nanoparticles with diameters of 4.2 nm, 5.9 nm, and 8.5 nm with low polydispersity were synthesized (figure 1a). Additionally, several complexes were successfully prepared, allowing one or two available coordination sites toward the nanoparticles surface (figure 1b). In the case of [CoII(TPMA)Cl2] complexes (TPMA: tris(2- pyridylmethyl)amine), a first evidence of the role of surface functionalization is given by the variation of hydrodynamic diameter versus the functionalization rate. When normalized to the diameter of particles, a domain with good colloidal stability is revealed for less than 1.8 complexes per nm2 (figure 2a). In this range of surface functionalization, a significant and progressive increase of the magnetic anisotropy (coercive fields measured at 5 K and blocking temperatures determined with zero-field-cooled and field-cooled curves) was obtained, and directly correlated to the amount of complexes at the surface of the nanoparticles (figure 2b). Besides, element-specific X-ray Absorption Spectroscopy (XAS) and X-ray Magnetic Circular Dichroism (XMCD) reveal the existence of a room-temperature persistent magnetic interaction between the complexes and the nanoparticles as the possible origin of the enhancement effect. Our strategy is thus unique to tune the enhancement of the anisotropy in iron oxide nanoparticles.
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Yoann Prado, Nielie Daffe,, Aude Michel, Thomas Georgelin, Nader Yaacoub et al.
Nature Communications, Nature Publishing Group, 2015, 6, pp.10139.
GDR MCM, Décembre 2013, Dourdan, France, communication orale : Modulation de l’anisotropie de particules magnétiques par des complexes magnétiques moléculaires. Y. Prado, A. Michel, B. Fleury, V. Dupuis, L. Lisnard, J. Fresnais.
Soleil User’s meeting satellite workshop, High Resolution Spectroscopies and Applied Science, Janvier 2016, Saint-Aubin, France, communication orale : Molecule-based anisotropy enhancement of superparamagnetic nanoparticles. Y. Prado, N. Daffé, A. Michel, T. Georgelin, N. Yaacoub, J.-M. Grenèche, F. Choueikani, E. Otero, P. Ohresser, M.-A. Arrio, C. Cartier-dit-Moulin, P. Sainctavit, B. Fleury, V. Dupuis, L. Lisnard, J. Fresnais.
GDR MCM2, Décembre 2015, Dourdan, France, communication par affiche : Molecule-based anisotropy enhancement of superparamagnetic nanoparticles. Y. Prado, N. Daffé, A. Michel, T. Georgelin, N. Yaacoub, J.-M. Grenèche, F. Choueikani, E. Otero, P. Ohresser, M.-A. Arrio, C. Cartier-dit- Moulin, P. Sainctavit, B. Fleury, V. Dupuis, L. Lisnard, J. Fresnais.
ICMM 2016 satellite meeting, Molecular technology for the design and control of functionalities in materials, Septembre 2016, Tokyo, Japon, communication orale : Molecule-based anisotropy enhancement of superparamagnetic nanoparticles. Y. Prado, N. Daffé, A. Michel, T. Georgelin, N. Yaacoub, J.-M. Grenèche, F. Choueikani, E. Otero, P. Ohresser, M.-A. Arrio, C. Cartier-dit-Moulin, P. Sainctavit, B. Fleury, V. Dupuis, L. Lisnard, J. Fresnais.
ICMM 2016, 15th International conference on molecule-based magnets, Septembre 2016, Sendai, Japon, communication par affiche : Molecule-based anisotropy enhancement of superparamagnetic nanoparticles. Y. Prado, N. Daffé, A. Michel, T. Georgelin, N. Yaacoub, J.-M. Grenèche, F. Choueikani, E. Otero, P. Ohresser, M.-A. Arrio, C. Cartier-dit-Moulin, P. Sainctavit, B. Fleury, V. Dupuis, L. Lisnard, J. Fresnais.
GDR MCM2, Décembre 2016, Dourdan, France, communication orale : Fonctionnalisation de nanoparticules magnétiques par des complexes moléculaires. Y. Prado, T. Georgelin, M.-A. Arrio, P. Sainctavit, C. Cartier-dit- Moulin, B. Fleury, V. Dupuis, L. Lisnard, J. Fresnais.
GDR MCM2, Novembre 2017, Dourdan, France, communication orale : Fonctionnalisation de nanoparticules magnétiques par des complexes moléculaires. Y. Prado, T. Georgelin, M.-A. Arrio, P. Sainctavit, C. Cartier-dit- Moulin, B. Fleury, V. Dupuis, L. Lisnard, J. Fresnais.
Congrès Gecom-Concoord 2017, Forges-les-Eaux, France, communication orale : Exaltation de l’anisotropie magnétique de nanoparticules superparamagnétiques par des molécules. Y. Prado, N. Daffé, A. Michel, T. Georgelin, N. Yaacoub, J.-M. Grenèche, F. Choueikani, E. Otero, P. Ohresser, M.-A. Arrio, C. Cartier-dit-Moulin, P. Sainctavit, B. Fleury, V. Dupuis, L. Lisnard, J. Fresnais.
Journée Soleil@UPMC, 6 novembre 2017, Exaltation de l’anisotropie magnétique de nanoparticules superparamagnétiques par des molécules, Y. Prado, N. Daffé, A. Michel, T. Georgelin, N. Yaacoub, J.-M. Grenèche, F. Choueikani, E. Otero, P. Ohresser, M.-A. Arrio, C. Cartier-dit-Moulin, P. Sainctavit, B. Fleury, V. Dupuis, L. Lisnard, J. Fresnais.
Workshop « Matériaux hybrides et systèmes de basse dimensionnalité à effets électroniques et magnétiques remarquables » par les Labex MiChem et Matisse, 15 Juin 2018, Paris, France, communication orale : Molecule-based anisotropy enhancement of superparamagnetic nanoparticles. Y. Prado, A. Michel, E. Otero, P. Ohresser, M.-A. Arrio, P. Sainctavit, C. Cartier-dit-Moulin, B. Fleury, V. Dupuis, L. Lisnard, J. Fresnais.
ACIN 2018, 4th international conference on advanced complex inorganic nanomaterials, Namur, Belgique, communication orale : Molecule-based anisotropy enhancement of superparamagnetic nanoparticles. Y. Prado, A. Michel, E. Otero, P. Ohresser, M.-A. Arrio, P. Sainctavit, C. Cartier-dit-Moulin, B. Fleury, V. Dupuis, L. Lisnard, J. Fresnais.

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