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.

Fe microflakes with uniform size and well-defined shape were successfully synthesized by hydrogen-thermal reduction of α-Fe₂O₃ precursor microflakes. The hexagonal Fe microflakes have edge lengths of about 5 μm and thicknesses of about 500–1000 nm. The complex permittivity and permeability of Fe microflakes–paraffin composite were measured using a vector network analyzer in the 2–18 GHz frequency range. Remarkable dielectric relaxation, natural resonance and exchange resonance were observed in the complex permittivity and permeability spectrum. Electromagnetic wave absorption (EMA) performance of samples was evaluated by using transmission line theory. An excellent microwave absorption performance was obtained for a coating containing Fe microflakes as filler, in which the maximum reflection loss is −15.3 dB and effective EMA band (RL < −10 dB) covers the whole frequency range of 12.2–16.6 GHz.