Rational A‐Site Entropy Engineering in Perovskites: Dual‐Exchange Enhanced Magnetoelectric Coupling for Ultra‐Efficient Microwave Absorption

High‐entropy engineering at the A‐site, combined with the variable valence states of Mn ions and diverse bonding configurations of perovskite elements and structures, presents new opportunities for the development and application of high‐temperature electromagnetic wave‐absorbing materials. In this study, the magnetic and dielectric properties of AMnO 3 are controlled by designing A‐site elements with various ionic radii and entropies. The microwave‐absorption performance of (La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 Na 0.2 )MnO 3 high‐entropy perovskites is significantly higher than those of AMnO 3 with different ionic radii and (Ba 1/3 Sr 1/3 Ca 1/3 )MnO 3 medium‐entropy perovskites. Specifically, the high‐entropy samples exhibit a minimum reflection loss (RL min ) of −60.86 dB at a thickness of 1.0 mm and an effective absorption bandwidth of 3.26 GHz, whereas the medium‐entropy ceramics show RL min values of −17.93 and −44.59 dB at 8.5 mm ((Ba 1/3 Sr 1/3 Ca 1/3 )MnO 3 ) and 8.8 mm ((La 0.25 Ba 0.25 Sr 0.25 Ca 0.25 )MnO 3 ), respectively. In high‐entropy perovskites, aliovalent ions and oxygen vacancies at the A‐site promote exchange interactions between Mn─O─Mn bonds, enhancing magnetism. Additionally, oxygen vacancies and lattice distortions in high‐entropy systems enhance the dielectric loss, achieving magnetoelectric cooperative coupling in high‐entropy perovskites. This work provides a new research direction for designing single‐phase perovskites with excellent electromagnetic wave‐absorbing properties via magnetoelectric cooperative‐loss coupling.