Magnetic properties and microwave absorption characteristic of MWNT filled with magnetite coated iron nanoparticles

Abstract

In this study, the measurement of magnetic and microwave absorption characteristics of MWNT (multi-walled carbon nanotubes) filled with Fe3O4 coated α-Fe nanoparticles and synthesized by dry mill using high energy milling have been performed. The sample was prepared from mixing of Fe and MWNT with a ratio of 10:1, then milled for 0, 5, 10, 15, 20, and 25 h respectively. The refinement results of X-ray diffraction pattern show that the sample have be formed MWNT/α-Fe@Fe3O4 nanocomposite which consists of C, α-Fe and Fe3O4 phases. Increasing milling time would generate an increasingly large α-Fe@Fe3O4 composite due to oxidation effect on the α-Fe powders surface. The morphologies of α-Fe@Fe3O4 particles were observed by TEM (Transmission Electron Microscopy) measurements. The particles, with lengths of up to at least 20 nm, have easily penetrated the nanotube cavity. The magnetic properties measurements show that the MWNT/α-Fe@Fe3O4 nanoparticles have a low coercivity field and a high remanence magnetization. The reflection loss of MWNT/α-Fe@Fe3O4 nanoparticles increases with increasing milling time. The MWNT/α-Fe@Fe3O4 nanocomposite achieves a reflection loss below −10 dB (70% absorption) at 10–11 GHz, and below −15 dB (80% absorption) at 12–13 GHz. Meanwhile the microwave absorbing peaks of composites containing MWNT/α-Fe@Fe3O4 nanoparticles shift to lower frequencies with increasing milling time.