Nature Communications : Enhancing the magnetic anisotropy of maghemite nanoparticles via the surface coordination of molecular complexes

Published on : 19/12/2016

Enhancing the magnetic anisotropy of maghemite nanoparticles via the surface coordination of molecular complexes, Nature Communications 6, doi:10.1038/ncomms10139

Prado Y., Daffé N., Michel A., Georgelin T., Yaacoub N., Grenèche JM, Choueikani F., Otero E., Ohresser P., Arrio MA., Cartier-dit-Moulin C., Sainctavit Ph., Fleury B., Dupuis V., Lisnard L., Fresnais J.

Contact PHENIX : Jerome Fresnais

Abstract :
Owing to their magnetic properties, iron oxide nanoparticles are of considerable interest for applications in high-density data storage or in medicine.1,2 In the case of small particles though, the so-called superparamagnetic limit is reached and the relevant magnetic properties lost.3 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 magnetic anisotropy. Modifying it represents thus one of the best approaches to improve the properties.
To enhance the anisotropy of sub-10 nm nanoparticles we have been investigating a novel synthetic strategy. It consists in the elaboration of composite materials where anisotropic molecular complexes are coordinated to the surface of the nanoparticles. Reacting 5 nm \gamma-Fe2O3 nanoparticles with the [CoII(TPMA)Cl2] complex (TPMA : tris(2-pyridylmethyl)amine) has led to the desired composite materials. The functionalised nanoparticles have been characterised with various techniques, evidencing the successful coordination –without nanoparticle aggregation and without complex dissociation– of the molecular complexes to the nanoparticles surface. SQUID and Mössbauer measurements indicate the significant enhancement of the anisotropy in the final objects. Indeed, the functionalised nanoparticles show a three-fold increase of the blocking temperature and a coercive field increased by one order of magnitude.
1 Fuji Electric Review, 2011, 57.
2 N. A. Frey, S. Peng, K. Cheng and S. Sun, Chem. Soc. Rev., 2009, 38, 2532–2542.
3 V. Skumryev, S. Stoyanov, Y. Zhang, G. Hadjipanayis, D. Givord and J. Nogués, Nature, 2003, 423, 850–853.