Ideal electromagnetic attenuation material should not only shield the
electromagnetic interference but also need strong absorption. Lightweight microwave
absorber with thermal stability and high efficiency is a highly sought-after goal of
researchers. Tuning microwave absorption to meet the harsh requirements of thermal
environments has been a great challenge. Here, grape-like Fe3O4-multiwalled carbon
nanotubes (MWCNTs) are synthesized, which have unique multiscale-assembled
morphology, relatively uniform size, good crystallinity, high magnetization, and favorable
superparamagnetism. The Fe3O4-MWCNTs is proven to be a smart microwave-absorber
prototype with tunable high intensities in double belts in the temperature range of 323−
473 K and X band. Maximum absorption in two absorbing belts can be simultaneously
tuned from ∼−10 to ∼−15 dB and from ∼−16 to ∼−25 dB by varying temperature,
respectively. The belt for reflection loss ≤−20 dB can almost cover the X band at 323 K.
The tunable microwave absorption is attributed to effective impedance matching,
benefiting from abundant interfacial polarizations and increased magnetic loss resulting from the grape-like Fe3O4 nanocrystals.
Temperature adjusts the impedance matching by changing both the dielectric and magnetic loss. The special assembly of
MWCNTs and magnetic loss nanocrystals provides an effective pathway to realize excellent absorbers at elevated temperature