Fe/Co ratio dependent excellent microwave absorption of FeCo alloys with a wide bandwidth in the high-frequency region

FeCo nanoparticles with nearly the same particle size and different compositions are prepared using a polyol method. The Co content of the FeCo nanoparticles influenced the magnetic and electromagnetic properties. Impedance matching is highly correlated with Co content, and the best composition can be obtained at Fe51Co49 (S5) and Fe38Co62 (S6) with a high magnetic loss, dielectric loss, and attenuation constant. The optimal reflection loss (RL) values of S5 and S6 are -59 dB at 13.28 GHz with a thickness of 1.4 mm and -51 dB at 14.55 GHz with a thickness of 1.4 mm, respectively, while the bandwidth, indicating a range of less than -10 dB, is 5.34 GHz (11.07−16.41 GHz) and 6.31 GHz (11.13−17.44 GHz), respectively. Thus, the high performance, which originates from an outstanding magnetic and dielectric loss, can be applied to S5 and S6 as a high-frequency electromagnetic wave absorbent.