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Controlled synthesis of core–shell iron–silica nanoparticles and their magneto-dielectric properties in polymer composites

Low loss core–shell iron–silica nanocomposites with improved magneto-dielectric properties at radio frequencies (1 MHz–1 GHz) were successfully fabricated. A new simple method was developed to synthesize metallic iron (Fe) nanoparticles with uniform size distribution in an aqueous environment at room temperature. Citric acid and oleic acid served as surface-capping agents to control the particle size of the synthesized Fe nanoparticles. Smaller Fe nanoparticles with narrower particle size distribution were obtained as the concentration ratio of iron ions to carboxylic acid groups decreased. The Fe nanoparticles were subsequently coated with silica (SiO2) layers to prevent the iron cores oxidizing. Polymer composites were prepared by incorporating Fe@SiO2 nanoparticles with polydimethylsiloxane (PDMS) elastomers. Experimental results showed that the dielectric permittivity (ε) and magnetic permeability (μ) of the polymer composite increased with increasing amount of Fe@SiO2 nanoparticle doping. The dielectric loss (tanδ) was near 0.020 at a frequency of 1 GHz.