O-Centered Asymmetric Electric Field Enables Broadband Electromagnetic Wave Absorption of Medium-Entropy Spinel Ferrite (Mg0.5Fe0.5)(NiMn)O4

Spinel ferrites are promising candidates for electromagnetic wave (EW) absorption, yet their practical application is severely constrained by a narrow effective absorption bandwidth (EAB), primarily caused by impedance mismatch at the EW incidence interface. The key to addressing this issue lies in balancing the weak dielectric loss and strong magnetic loss within the spinel lattice, which is desirable yet challenging. Herein, we design a medium-entropy spinel ferrite (Mg0.5Fe0.5)(NiMn)O4 and leverage the O-centered asymmetric electric field induced by the medium-entropy configuration to break such a barrier. Combined with comprehensive electronic structure characterization and density functional theory calculations, we clarify that the O-centered asymmetric electric field is induced by the medium-entropy configuration, which gives rise to impurity states near the Fermi level, dipole centers, and an enhanced net magnetic moment, ultimately enabling synergistic dielectric-magnetic optimization and improved impedance matching. Consequently, compared with NiFe2O4, (Mg0.5Fe0.5)(NiMn)O4 exhibits broadband electromagnetic wave absorption characteristics and achieves a minimum reflection loss of -57.19 dB at 8.08 GHz (256% enhancement) with an effective absorption bandwidth of 4.48 GHz (367% increase). In addition, through constructing gradient multilayer periodic arrays using (Mg0.5Fe0.5)(NiMn)O4, the EAB is further broadened from 4.48 to 13.09 GHz (covering 4.91-18 GHz). These insights reveal the mechanism of the O-centered asymmetric electric field in medium-entropy spinel ferrite for broadband absorption and provide a rational strategy for designing high-performance spinel ferrite-based electromagnetic wave absorbing materials.