Infrared extinction and microwave absorption properties of hybrid Fe₃O₄@SiO₂@Ag nanospheres synthesized via a facile seed-mediated growth route

Fe₃O₄@SiO₂@Ag ternary hybrid nanoparticles were synthesized via a facile seed-mediated growth route. X-ray diffraction, transmission electron microscopy and vibrating sample magnetometer measurements were used to characterize the as-prepared product. The results indicated that the nanoparticles exhibited excellent magnetic properties and an extremely dense structure with Ag layer thicknesses of 30, 40, and 50 nm. Furthermore, the microwave shielding effectiveness exceeded 20 dB over almost the entire frequency range (2-18 GHz), and the effectiveness obviously improved as the thickness of the Ag layer increased. In addition, the IR extinction coefficient of the nanoparticles was calculated by a finite-difference time-domain method, which showed that the nanoparticles can inherit the extinction performance of pure silver when the Ag shell thickness was 30 nm. Specifically, after assembling into chains, the peak position of the IR extinction curves displayed a significant redshift and an intensity increase as the number of nanoparticles increased in the chain, which dramatically promoted the IR extinction capability. As a result, the Fe₃O₄@SiO₂@Ag nanoparticles are expected to be used as a new multispectral interference material.