Electronic Transport and Magnetic Properties of Co/SiO2 Magnetic Nanocomposites

Electric, thermoelectric, and magnetic properties of the magnetic nanocomposite (MNC) Co/SiO2 consisting of nanometer-size Co nanoparticles embedded in SiO2 dielectric matrix have been studied. MNC is obtained in the form of (0.8-2.3)mu m thick films with Co concentration 31.7-65.4at.% by the electron beam physical vapor deposition method on polycrystalline Al2O3 substrates. The temperature dependence of the resistivity follows the Mott law. The negative magnetothermoelectric power discovered in MNC Co/SiO2 can be explained by hopping conductivity through the magnetic localization centers in the SiO2 matrix or chemical interaction of Co with Si and O-2, which results in a mixture of CoSi (ferromagnetic) and CoO (antiferromagnetic) phases. As the cobalt concentration increases, the particle size increases and the interparticle distances decrease. This is confirmed by the magnetic behavior of the sample with high Co concentration, which is dominated by large Co nanoparticles and strong interparticle magnetic interactions.