The influence of silica matrix on the crystal structure and high frequency performance of cobalt nanoparticles

Cobalt-SiO₂ nanocomposites were successfully synthesized by chemical precipitation combined H₂ reduction method. The influence of SiO₂ matrix on the crystal structure and high frequency magnetic properties of cobalt nanoparticles was investigated. Amorphous SiO₂ layer, which is adhered to Co particle surface through Si-O-Co bonds, inhibits the growth of the nanoparticles and stabilizes the face-centered-cubic (FCC) structured Co. The FCC-cobalt/SiO₂ nanocomposites exhibit soft magnetic behavior with saturation magnetization (M_s) about 125 emu/g and coercivity (H_c) smaller than 100 Oe. The permeability spectra of Co/SiO₂ nanocomposites depend on the SiO₂ contents. When the SiO₂ content is greater than 8 wt%, the permeability spectra demonstrate notable high frequency characteristic, in which the real part μ′ of the permeability is almost independent of frequency and the imaginary part μ″ remains extremely low in high frequency range.