Hydrothermal synthesis of polyhedral FeCo alloys with enhanced electromagnetic absorption performances

Polyhedral FeCo alloys with grain sizes of 1–2 μm were synthesized by using a low-temperature hydrothermal method. The effects of heating time and molar ratio on microstructure and electromagnetic absorption performances of the alloys were studied. Their growth follows the Ostwald ripening mechanism. At the given reaction time of 10 h, as the molar ratio of Fe:Co was varied from 3:7 to 4:6, morphology of the alloy particles was changed from flower-like to polyhedral shape. Specifically, the Fe6Co4 sample had superior impedance matching, while a strong dielectric resonance at about 10 GHz was observed in the complex dielectric constant imaginary part, thus resulting in significantly enhanced electromagnetic absorption performance. It exhibited an optimum reflection loss (RL) value of −52.20 dB at 10.48 GHz, with a sample thickness of 1.7 mm. Meanwhile, the RL of −10 dB was over the frequency range of 7.6–13.6 GHz, covering the Ku-band and the entire X-band. Most importantly, the matching thickness of all the samples was less than 2 mm. These results indicate that the FeCo alloy particles are suitable for electromagnetic absorbing materials at the C, X and Ku bands.