Structural analysis and magnetic-microwave absorption properties of natural mineral-derived silica-coated magnetite nanocomposites

Herein, a green synthesis method to prepare silica-coated magnetite nanocomposites by employing ironstone (an Indonesian natural resource) and an industrial by-product of zircon sand purification is reported. The X-ray diffraction pattern confirmed the formation of the magnetite phase, with an increased lattice constant after the coating process. The absorbance peaks of Fourier transform infrared spectra and the clear boundary in high-resolution transmission electron micrographs suggested that no chemical reaction was involved between Fe₃O₄ and SiO₂. Silica coating caused a decrease in magnetic saturation and initial susceptibility and an increase in the coercivity, remanence, and domain magnetic size of composites. The microwave absorption peaks for SiO₂ and Fe₃O₄ nanoparticles were observed at approximately 10.00 and 11.00 GHz, respectively. Fe₃O₄/SiO₂ nanocomposites exhibited both absorption peaks with improved absorption and a tunable frequency. Furthermore, the combination of Fe₃O₄ as a magnetic and SiO₂ as a dielectric material provided an advantage in adjusting the direction of the magnetic dipole moment and electric dipole polarization for specific applications.