Morphological and magnetic properties of Co nanoparticle thin films grown on Si3N4

The morphological and magnetic properties of Co nanoparticles deposited by triode sputtering on Si3N4 at 550 °C are reported. The nominal thickness of Co ranges from 2 up to 15 nm, and two different capping layers, Au and Pt, are used. The nanoparticles were characterized by x-ray diffraction and atomic force microscopy. Morphological and structural studies show that the nanoparticles grow in a well-defined nanostructured pattern and adopt a hexagonal closed packed crystalline structure. Moreover, the average particle size and the particle size dispersion increase as the thickness increases, due to percolation. Experimental characterization of effective anisotropy field was carried out with transverse susceptibility. Transverse susceptibility measurements reveal an in-plane isotropic magnetic behavior. Both the effective anisotropy field and the coercive field increase as the particle size increases, following a D6 dependence, which is typical for three-dimensional structures in the framework of the random anisotropy model. The relationship between the particle size distribution and the anisotropy field distribution is shown, explaining the significant dependence of the magnetic behavior on the Co layer thickness. On the other hand, different capping layers give rise to a change in the magnetic response due to the modification of the interparticle interaction.This work was supported in part by Universidad de Oviedo. One of the authors (B.P.) gratefully thanks Dr. Luis Eugenio Fernandez-Outon and Dr. Gonzalo Vallejo- Fernandez for the support received in the particle size analysis. Also, B.P. acknowledges financial support received from Gobierno del Principado de Asturias under Grant No. BP05-015. J.M.G.M. wishes to thank the financial support from CSIC under Project No. PIE 200650 130. C.C. acknowledges the Ministerio de Educación y Ciencia and FPI program for financial support.Peer reviewe