Magnetic anisotropy of embedded Co nanoparticles: Influence of the surrounding matrix

We report on the magnetic properties of Co clusters embedded in four different matrices (Ag, Au, Si, and amorphous carbon). The recently developed triple fit method for treating conventional magnetometry data allows, together with micro-superconducting quantum interference device (mu-SQUID) investigations, the detailed study of the influence of the surrounding matrix on the magnetic volume and the magnetic anisotropy of Co nanoparticles. While interdiffusion between matrix and Co atoms cannot be excluded in Si and amorphous C matrices, the structure of clusters embedded in the metallic matrices remains intact. Ag and Au matrices increase significantly the magnetic anisotropy energy of the Co clusters. mu-SQUID experiments indicate that the magnetic anisotropy of embedded clusters is not affected by a magnetically dead layer and that an anisotropy dispersion must be taken into account for size-selected nanoparticles.