Iron deficiency strategy toward single-phase high-entropy M-type ferrites for broadband millimeter-wave absorption with low thickness

Electromagnetic pollution and radiation now extend to encompass millimeter waves, while the development of broadband millimeter-wave absorbers remains significantly hindered by lacking efficient loss mechanisms. High-entropy M-type ferrites are promising due to their excellent magnetic resonance and dielectric polarization, yet precise electromagnetic parameter regulation remains challenging because intermediate-phase impurities persist from insufficient configurational entropy. Herein, we propose an iron-deficient strategy to synthesize the single-phase Zr4+-doped high-entropy M-type ferrites. It is found that iron deficiency eliminates impurities by enhancing entropy and provides a more adaptable local structure. The synergistic effect of high entropy and iron deficiency amplifies the dielectric loss capacity, while Zr4+ doping broadens the magnetic loss range by modulating natural resonance. This yields an ultra-broad absorption bandwidth of 12.18 GHz and ultra-thin matching thickness below 1 mm within the millimeter-wave atmospheric window around 35 GHz, offering insights for absorbers against electromagnetic pollution and radar stealth. Single-phase high-entropy M-type ferrites have been synthesized successfully via an iron deficiency strategy, achieving a broad millimeter-wave absorption bandwidth of 12.18 GHz around 35 GHz with thickness below 1 mm.