Co/C nanoparticles with low graphitization degree: A high performance microwave-absorbing material

Co/C nanoparticles (NPs) with a size of 45 nm have been prepared by an arc plasma method under a mixed methane and argon atmosphere. They display a uniform carbon shell of 3 nm in thickness and have a low graphitization degree. The saturation magnetization (M_S) and coercivity (H_C) of the NPs are 159.9 emu g^-1 and 275.7 Oe, respectively. The microwave absorption properties of the Co/C NPs mixed with paraffin wax (PW) at 25, 50 and 75 wt% NPs have been investigated in the range of 2-18 GHz. The Co/C-PW composite with 50 wt% NPs exhibits the best microwave absorption performance. It has a minimum reflection loss (RL) value of -43.4 dB at a thickness of 2.3 mm, and the absorption bandwidth for RL ≤ -20 dB is as large as 7.2 GHz, which is the highest value among the reported Co-based absorbers. The high microwave absorption performance is interpreted in terms of impedance matching, core/shell structure and nanosize effects. The carbon-coated magnetic metal NPs prepared by methane plasma arc are potential microwave absorbers with strong absorption intensity and wide absorption bandwidth.