Magnetite nanocrystals on multiwalled carbon nanotubes as a synergistic microwave absorber

The understanding of the interaction between the building blocks in the hybrids can advance our comprehension of design principles in high-performance microwave absorbing materials. Here, we report a hybrid material consisting of magnetite (Fe₃O₄) nanocrystals grown on multiwalled carbon nanotube (MWCNT) as a high-performance microwave absorber in the 2-18 GHz band, although Fe₃O₄ nanocrystals or MWCNTs alone or their physical mixture show little microwave absorption. The hybrid is characterized by transmission electron microscopy, X-ray diffraction, and vector network analysis, X-ray absorption near-edge structures at the C K-edge and Fe L _3,2-edge, and electron spin resonance analysis. Microstructural analysis reveals that Fe₃O₄ nanocrystals are immobilized on the MWCNT surface by a strong interaction. Charges in the MWCNT/Fe ₃O₄ hybrids transfer from the conduction band in Fe ₃O₄ to C 2p-derived states in the MWCNT substrate. Dipole interaction between the magnetic nanocrystals is increased. The synergetic interactions leads to much improved microwave absorption.