Superparamagnetic Fe3O4/MWCNTs heterostructures for high frequency microwave absorption

Abstract

Superparamagnetic Fe₃O₄ nanocrystals anchored on multiwalled carbon nanotubes (MWCNTs) were fabricated via a straightforward co-precipitating technique which nicely integrates the magnetic and dielectric components into a synergistic microwave absorber. A complex permeability analysis indicates that the resonance frequency of Fe₃O₄/MWCNTs heterostructures appears at 9.1 GHz relying on superparamagnetic relaxation, which is much higher than that of conventional Fe₃O₄ ferromagnetic particles. As a result of the blue-shift of the resonance frequency, the Fe₃O₄/MWCNTs nanocomposites exhibit remarkably improved microwave absorption performances in a high frequency range (Ku-band). Moreover, combing the synergistic effect between ultra small Fe₃O₄ nanocrystals and MWCNTs, the Fe₃O₄/MWCNTs hybrids exhibit a bandwidth of frequency less than −20 dB, almost covering the whole 2–18 GHz range by adjusting the absorber thickness. The results provide a new approach to enhance the resonance frequency break of the Snoek limit, which significantly optimizes microwave absorption ability for high frequency applications.