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_0.4Mo_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.