Strong dual-frequency electromagnetic absorption in Ku-band of C@FeNi3 core/shell structured microchains with negative permeability

•C@FeNi3 core/shell structured microchains were obtained by a simple hydrothermal method.•C@FeNi3 core/shell structured microchains exhibit strong dielectric relaxation over 12–18 GHz, which corresponds to the Debye dipolar relaxation.•Complex permeability has negative imaginary parts within 11.5–18 GHz, owing to the peculiar chains like structures.•Enhanced dual-frequency EMA performance was observed in 12–18 GHz due to interface relaxation and proper electromagnetic matching.

C@FeNi3 core/shell structured microchains with an average diameter of 400 nm and lengths of about tens microns were synthesized by a simple hydrothermal method. The morphologies, microstructures and electromagnetic properties were investigated by means of scanning electron microscope, transmission electron microscopee, X-ray diffraction, Raman spectroscopy, physical property measurement system and vector network analyzer. C@FeNi3 core/shell structured microchains were constructed by FeNi3 alloy submicron spheres with average diameter of 350 nm and carbon shell with thickness about 50 nm. Their electromagnetic properties were investigated in the 2–18 GHz frequency range. The permittivity presented strong dielectric relaxation behavior over 11.5–18 GHz, corresponding to Debye dipolar relaxation. The permeability was found to have negative imaginary parts within 11.5–18 GHz. Strong dual-frequency absorption behavior was observed in the Ku-band due to consequence of interface relaxation.