Unveiling the Synergistic Mechanisms for Ultrahigh Plasticity and Soft Magnetism in Fe‐Co‐Ni‐Al‐Cu‐Mo High‐Entropy Alloys

This study focuses on Fe‐Co‐Ni‐Al‐Cu‐Mo system high‐entropy alloys (HEAs), aiming to address the challenge of achieving synergistic optimization of “magnetic properties‐mechanical properties properties” in traditional soft magnetic materials. By designing the Fe 45 Co 30 Ni 10 Al 7 Cu 3 Mo 5 (Mo5) high‐entropy alloy and combining characterization techniques such as XRD, SEM, TEM, EBSD, MFM, and DFT calculations, the correlation between its microstructure and properties was systematically investigated. The results show that the Mo5 alloy forms a fine and uniform multiphase structure dominated by the BCC phase (85.4%) with the presence of σ phase (13.5%). This structure enables an excellent strength‐ductility balance, achieving over 100% plasticity and a yield strength of 763 MPa. The underlying mechanisms include grain refinement strengthening, diffusion‐assisted grain boundary sliding promoted by semicoherent interfaces, and dynamic dislocation recovery. In terms of soft magnetic properties, the Mo5 alloy exhibits a saturation magnetization of 117.6 emu/g and a coercivity of 16.83 Oe. The σ phase and fine grain boundaries enhance coercivity through magnetic domain pinning. Although Mo‐induced orbital hybridization weakens local magnetic moments, the significant difference in spin density of states still maintains strong magnetism in the alloy. This study provides a theoretical basis for the synergistic regulation of “magnetism‐mechanics properties” in high‐entropy alloys.