Magnetism and magneto-optics of Co nanoparticles embedded in dielectric and metallic matrices

We present a structural, magnetic and magneto-optical (MO) study of Co nanoparticles sputter-deposited at different temperatures and embedded in three different matrices (two insulators such as MgO and AlN and a metal such as Pt). MgO capping layer does not affect the magnetism of the nanoparticles as demonstrated by in situ transversal and ex situ polar Kerr loops. The structure of the nanoparticles was investigated by TEM and a Co crystalline core surrounded by an amorphous crust was observed. From the analysis of the MO spectral response of the nanoparticles we demonstrate that the evolution of the MO constants as a function of Co concentration can be explained with the Maxwell-Garnett model. It is also observed that the reduction of nanoparticles size gives rise to a decrease of the relaxation time of the electrons into them. The deposition of Pt capping gives rise to the magnetic connection of the islands mediated by the polarised K with the formation of different Co-Pt compounds as was observed with TEM. We observe that in the case of AIN capping destroys the magnetism of the samples due to a strong nitridation of Co.