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 (Ms) about 125 emu/g and coercivity (Hc) 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.