Dynamic Phase Transition Driven Achievement of Ultra‐Broadband Microwave Absorption in FeCoNiCrMo High‐Entropy Alloys

Although soft magnetic high‐entropy alloys (HEAs) offer the advantage of broadband absorption in microwave absorption materials, it remains challenging to simultaneously enhance their saturation magnetization (M s ) and coercivity (H c ). This trade‐off limits further improvements in both the permeability and effective absorption bandwidth (EAB). This work addresses this challenge by regulating the phase composition and tailoring H c of FeCoNiCr 0.4 Mo 0.1 HEAs through thermal annealing. Precisely controlled annealing induces the precipitation of strongly ferromagnetic α‐Fe phase, realizing the phase transformation of HEAs from a single FCC phase to FCC/BCC dual‐phase structure. The precipitation of α‐Fe not only enhances M s but also effectively modulates H c by introducing magnetic domain wall pinning sites at the FCC/BCC interfaces. The optimization, combined with the enhanced magnetic anisotropy and interface polarization effect derived from phase regulation, forms a synergistic magnetic‐dielectric loss mechanism. This mechanism enables the A500 HEAs to achieve an ultra‐broad EAB of 7.4 GHz at an ultrathin thickness of 1.4 mm. The A500 coating with a thickness of 1.17 mm achieves excellent absorption performance with EAB of 4.2 GHz. After 8 days of salt spray corrosion, the coating still maintains 3.1 GHz, demonstrating immense potential as a new generation of high‐performance electromagnetic absorption materials.