Excellent improvement in the static and dynamic magnetic properties of carbon coated iron nanoparticles for microwave absorption

Carbon coated iron nanoparticles were synthesized, using a simple arc-discharge method. The morphology and the internal structure of the core/shell nanoparticles were studied, using field emission scanning electron microscopy and transmission electron microscopy. X-ray diffraction analysis showed that both magnetic alpha-Fe and nonmagnetic gamma-Fe phases existed in the as-prepared particles. In order to improve the static and dynamic magnetic properties of the core/shell nanoparticles, the produced nanocapsules were annealed in argon atmosphere at two different temperatures. Hysteresis loops revealed that the value of the saturation magnetization (M-s) increased more than 4.1 times of its original value by annealing and this led to 70% increase in the imaginaiy part of the permeability. Phase analysis showed that heat treatment eliminated the nonmagnetic gamma-Fe phase completely. The reflection loss plots were studied for composite layers containing 20 vol% of the annealed and not annealed nanocapsules. One of the absorber layers which contained annealed nanocapsules showed at least -10 dB loss in the whole G, C, X and Ku frequency bands and the optimal absorption exceeded -37 clB at 5.8 GHz for the as-prepared sample with a thickness of 3.2 mm. The results revealed that the magnetic properties of the arc-made Fe/ C core/shell nanoparticle can be improved significantly by annealing in argon. (C) 2015 Elsevier B.V. All rights reserved.