Enhanced microwave absorption property of ferroferric Oxide: The role of magnetoelectric resonance

The modification of ferrites can effectively improve their microwave absorption (MA) properties. However, attempts to improve their high-frequency performance were still limited and considerably cumbersome for practical application. Herein, we present a facile method that effectively improves the MA behavior of Fe3O4 through direct fluorination using F-2/N-2 gas. Specifically, we fabricated core-shell structured fluorinated Fe3O4 (F-Fe3O4) with a fluorine-doped shell and an unmodified Fe3O4 core by carefully controlling the F-2 concentration and fluorination temperature. We found a unique 'magnetoelectric collaborative resonance' (MDR) effect in F-Fe3O4, manifested by the co-occurrence of double dielectric and magnetic resonance peaks at 14.8 and 16.6 GHz. Band gap measurements and molecular simulations results indicated that the smaller energy gap derived from fluorine doping facilitates both electron hopping between the mixed-valence Fe2+/Fe3+ states and electron accumulation at the core-shell interface, which induce simultaneous magnetic exchange interactions and the Maxwell-Wagner effect (interface polarization). As a result, the incident electromagnetic wave can be dissipated via magnetic exchange resonance coupled with dielectric resonance, thereby improving the MA properties at the same frequency of MDR. Compared with those of pristine Fe3O4, the minimum reflection loss of F-Fe3O4 was four times higher, reaching-64.9 dB, and the effective absorption bandwidth was 5.03 GHz, which is almost 1.6 times higher. We believe this facile and effective modification method and the unique loss mechanism of MDR will advance the structural design of high-performance MA materials.