Tuning the magnetic anisotropy of nanoparticles by metal cappingF. Luis1, F. Bartolomé1, F . Petroff2, 3, J. Bartolomé1, L. M. García1, C. Deranlot2, 3, H. Jaffrès2, 3, M. J. Martínez1, P. Bencok4, F. Wilhelm4, A. Rogalev4 and N. B. Brookes4
1 Instituto de Ciencia de Materiales de Aragón, CSIC-Universidad de Zaragoza and Departamento de Física de la Materia Condensada, Universidad de Zaragoza 50009 Zaragoza, Spain
2 Unité Mixte de Physique CNRS/Thales - Route Départementale 128 91767 Palaiseau Cedex, France
3 Université Paris-Sud - 91405 Orsay Cedex, France
4 European Synchrotron Radiation Facility - BP 220, F-38043 Grenoble, France
received 31 March 2006; accepted in final form 14 August 2006
published online 6 September 2006
The magnetic anisotropy of Co clusters with diameters ranging from 1.1 to 4.5 turns out to be significantly larger than in bulk and strongly increasing with decreasing cluster size. The dominating role of the surface can be used to modify the anisotropy by changing the electronic properties of the matrix surrounding the clusters. We find that capping the clusters by a metallic (Cu and Au) layer significantly enhances the anisotropy, thus also stabilizing the magnetization against thermal fluctuations. The observed anisotropy enhancement is attributed to the bonding of the Co 3d electrons to the conduction band of the capping layer, which depends on the electronic band structures of both metals.
75.50.Tt - Fine-particle systems; nanocrystalline materials.
75.70.-i - Magnetic properties of thin films, surfaces, and interfaces.
75.30.Gw - Magnetic anisotropy.
© EDP Sciences 2006