Extended Working Frequency of Ferrites by Synergistic Attenuation through a Controllable Carbothermal Route Based on...

One of the major hurdles of ferrite-based microwave absorbing materials is the limited working frequency that urgently calls for an effective modification technique. Herein, a controllable carbothermal route has been developed to ameliorate the microwave absorption performance of Fe₃O₄ nanospheres by using metal-organic frameworks (MOFs) shell as a carbon source with changing ramping rates. An enhanced synergistic attenuation induced by varied composition and tailored morphology is of great importance, which can be regarded as the superiority of the comprehensive (magnetic and dielectric), rather than unilateral (dielectric), modification technique. The drawbacks of dielectric modification can be concluded as the separated attenuation mechanisms at discrete frequencies, proven by the construction of the core-shell structured Fe₃O₄@Prussian blue composite. The advantages of magnetic modification can also be confirmed by a series of Fe-based composites with unique composition and tailored structure derived from the Fe₃O₄@Prussian blue composite at a distinct heating rate. Further, the superiority can be summarized as the rearrangement of magnetic loss by exceeding the Snoek limit and the reinforcement of dielectric loss by enhancing the electrical conductivity and introducing multiple polarization processes. Consequently, the sample obtained at 10 °C min^-1, which contains Fe and Fe₃O₄, shows an extended working frequency of 14.05 GHz, with a thickness less than 5 mm and a high reflection loss value of -48.04 dB at 1.55 mm. This work not only offers a novel carbothermal route based on MOFs coating to prepare desired magnetic composites, but also acquires deeper insights of the comprehensive modification technique, which may pave the way for designing high-performance electromagnetic devices.