The recent decades have shown that nanocrystals (NCs) can play an important role in a lot of different fields such as biology, catalysis, and magnetism. Functional materials displaying long-range ordered nanostructures are the focus of intensive research. For example, nanocrystals superlattices (NSLs) or binary nanocrystal superlattices (BNSLs) can be described as materials made of the periodical arrangement of single type nanocrystals or nanocrystals of different nature and/or size. [1] The self-assembly of nano-objects with various physical properties is an elegant and cheap bottom-up approach allowing to design multifunctional materials at the nanometric scale. Moreover, the highly ordered structure and well-defined stoichiometry of the superlattices permit a precise control of their properties. Soft chemistry allows synthesis of well-defined inorganic nanocrystals able to self-assembled in 2D or 3D superlattices. This is illustrated by reporting the first synthesis of pure mono-dispersed spherical hcp-nanocrystals ferromagnetic at room temperature. [2] Our strategy, based on the simple combination of chemical reagents allows the one-pot synthesis of size controlled hcp-nanocrystals. Size and shape of the nanocrystals can be tuned by varying the reaction time or the concentration. The choice of cobalt NCs results from their particular interest due to its high magneto-crystalline anisotropy in the hcp-structure. Furthermore, the combination of different inorganic components as magnetic nanocrystals and giant polyoxometalates (POMs) allows the formation of Multifunctionnal Nanostructured Material. The POMs inserted in octahedral interstices of superlattices of Magnetic Nanocrystals act as binder constituents, increasing the film cohesion and leading to an enhanced ordering of the nanocrystals. Hence, a structuring effect can be obtained while preserving the magnetic properties of gamma-Fe2O3 thanks to surfactant-induced weak interactions. In specific cases it is possible to increase the interparticle distance and consequently decrease dipole-dipole magnetic interactions. [3]

References.

[1] H. Brune, A. Courty, C. Petit and V. Repain “Self-assembly of nano-alloys in Nanoalloys: From Fundamentals to Emergent Applications”, Florent Calvo, Editors, Elsevier (2013).

[2] L. Mezziane, C. Salzemann, H. Gérard, C. Aubert, M. Petit, C.Petit. “Nanoparticules de cobalt ferromagnétiques à température ambiante, procédé de préparation et utilisations.” French Patent UPMC et CNRS le 9 décembre 2015 n°15 62083.

[3] R. Breitwieser, T.Auvray, F.Volatron, C.Salzemann, A.-T. Ngo, P.-A. Albouy, A. Proust, and C. Petit Small (2015), 12, 220