Microwave absorption properties of FeNi₃ submicrometre spheres and SiO₂@FeNi₃ core–shell structures

Nearly monodispersed FeNi₃ submicrometre spheres with an average diameter of 220 nm were synthesized by a simple low temperature reduction method. SiO₂@FeNi₃ core–shell structured submicrometre spheres with 25 nm thick SiO₂ shell were then fabricated by a sol–gel process. A significant enhancement of electromagnetic absorption (EMA) performance was achieved by the silica coating over the 2–18 GHz. The reflection loss (RL) exceeding −20 dB of the composite was obtained over 6.7–15.1 GHz by choosing an appropriate sample thickness between 2.1 and 3.3 mm, and an optimal RL of −61.3 dB was obtained at 8.7 GHz with a thin absorber thickness of 2.9 mm. The coating of the dielectric silica shell significantly enhanced the EMA performance due to the enhancement of interface polarization at the alloys and dielectric interfaces.