Strong microwave absorption of Fe@SiO2 nanocapsules fabricated by one-step high energy plasma

Abstract

Herein, the spherical Fe@SiO2 nanocapsules (NCs) has been synthesized by a one-step way of DC arc-discharge plasma under a mixture atmosphere of H2 and Ar. The high energy states of excited ions (Ar, H, Fe, Si) within plasma region are in situ recorded by online optical emission spectroscopy (OES) and become visible evidence for the energy conditions in the fabrication of Fe@SiO2 NCs. It indicates that the evaluated electron temperature of plasma reaches up to 3 × 104 K (∼2.6 eV) and can significantly influence the characters of the final product of Fe@SiO2 NCs. Magnetic measurement reveals that Fe@SiO2 NCs is dominant ferromagnetism exhibiting partial transition into superparamagnetism at TB = 160 K. Electromagnetic parameters (permittivity, permeability) in frequency range of 2–18 GHz show that an appropriate impedance matching has been established in Fe@SiO2/paraffin composite, which brings about excellent reflection loss (RL) of -61.6 dB at 9.3 GHz with thickness of 2.81 mm, and a wide bandwidth from 6 to 18 GHz with RL ≤ -10 dB. The significant impact of a SiO2 layer on the electromagnetic performances of Fe@SiO2 NCs has been emphasized here, with respect to behaviors of the counterpart, i.e. pure Fe nanoparticles (NPs).