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Size and shape effects on the order–disorder phase transition in CoPt nanoparticles

Nature Materials volume 8, pages 940–946 (2009)Cite this article

Abstract

Chemically ordered bimetallic nanoparticles are promising candidates for magnetic-storage applications. However, the use of sub-10 nm nanomagnets requires further study of possible size effects on their physical properties. Here, the effects of size and morphology on the order–disorder phase transition temperature of CoPt nanoparticles (TCNP) have been investigated experimentally, using transmission electron microscopy, and theoretically, with canonical Monte Carlo simulations. For 2.4–3-nm particles, TCNP is found to be 325–175 ∘C lower than the bulk material transition temperature, consistent with our Monte Carlo simulations. Furthermore, we establish that TCNP is also sensitive to the shape of the nanoparticles, because only one dimension of the particle (that is, in-plane size or thickness) smaller than 3 nm is sufficient to induce a considerable depression of TCNP. This work emphasizes the necessity of taking into account the three-dimensional morphology of nano-objects to understand and control their structural properties.

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Figure 1: Morphology of the particles projected in the substrate plane.
Figure 2: Structural analysis by TEM: experimental evidence for the size effect.
Figure 3: Monte Carlo simulations: numerical evidence for the size effect.
Figure 4: 3D morphology of the particles.
Figure 5: Shape effect on the structural properties of CoPt nanoparticles.

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Acknowledgements

We are grateful to Region Ile-de-France for convention SESAME 2000 E1435, for the support of the JEOL 2100F electron microscope installed at IMPMC (UMR 7590).

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Author notes

  1. D. Alloyeau

    Present address: Present address : Lawrence Berkeley National Laboratory (LBNL), National Center for Electron Microscopy (NCEM), 1 Cyclotron Road-MS, 72 Berkeley, California 94720, USA,

Authors and Affiliations

  1. Laboratoire Matériaux et Phénomènes Quantiques, Université Paris 7/CNRS, Bâtiment Condorcet, 4 rue Elsa Morante, 75205 Paris Cedex 13, France

    D. Alloyeau, C. Ricolleau, T. Oikawa, C. Langlois & N. Braidy

  2. Laboratoire d’Etude des Microstructures—ONERA/CNRS, B.P. 72, 92322 Châtillon, France

    D. Alloyeau, Y. Le Bouar, N. Braidy & A. Loiseau

  3. Centre Interdisciplinaire de Nanosciences de Marseille, CNRS, Campus de Luminy, Case 913, 13288 Marseille Cedex 9, France

    C. Mottet

  4. JEOL Ltd, 1-2 Musashino 3-Chome, Akishima, Tokyo 196-8558, Japan

    T. Oikawa

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Contributions

D.A. prepared the samples. D.A., C.R. and T.O. developed the STEM/NBD technique and carried out the TEM experiments. D.A. analysed the experimental data. C.M. carried out the Monte Carlo simulations and described them in the article. C.R., Y.L.B., C.L. and A.L. supervised the project. D.A. and C.R. prepared the manuscript. N.B. contributed to the energy-dispersive X-ray data analysis and improved the writing of the article. All authors discussed the results and implications and commented on the manuscript at all stages.

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Correspondence to D. Alloyeau.

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Alloyeau, D., Ricolleau, C., Mottet, C. et al. Size and shape effects on the order–disorder phase transition in CoPt nanoparticles. Nature Mater 8, 940–946 (2009). https://doi.org/10.1038/nmat2574

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