Defect-engineered high-entropy spinel ferrite nanofibers via Joule heating for superior microwave absorption

Spinel ferrites with exceptional magnetic permeability, optimal impedance matching, and robust chemical stability have attracted considerable attention in high-performance electromagnetic wave (EMW) absorption applications, yet their insufficient dielectric dissipation and constrained absorption bandwidth limit their use in advanced EMW absorption. Herein, an entropy-driven strategy based on electrospinning and the ultrafast Joule-heating method was designed to fabricate novel defect-rich (Mn_0.2Co_0.2Ni_0.2Cu_0.2Zn_0.2)Fe₂O₄ high-entropy spinel ferrite nanofibers (HESF NFs). The results demonstrate that the high configurational entropy of HESF NFs induces severe lattice distortions, abundant oxygen vacancies, and ultradense grain boundaries, significantly reinforcing dipole and interfacial polarization. The inherent conductive dissipation in the three-dimensional (3D) fibrous architecture and multiscale EMW scattering concurrently refine the impedance matching. The quantitative analysis suggests that the entropy-mediated lattice strain and oxygen vacancies govern charge redistribution. Density functional theory (DFT) calculations attribute the enhanced dielectric loss to bandgap narrowing and localized electronic states. All these features endow the resultant HESF NFs with advanced EMW performance, achieving a minimum reflection loss of −53.58 dB at 1.6 mm and an effective absorption bandwidth of 7.82 GHz at 1.8 mm. Overall, defect density plays a critical role in modulating EMW dissipation through Joule-heating technology and should be the focus for designing high-performance EMW absorbers based on HESF NFs.