Ultrahigh‐Strength Soft‐Magnetic NiFeCoAl Multi‐Principal Element Alloys Enabled by Multiscale Heterostructure Design

Soft‐magnetic materials (SMMs) are indispensable for electrification and sustainable energy systems, yet their inherent mechanical fragility fundamentally limits applications under severe mechanical stresses. Enhancing the yield strength of SMMs is essential to prevent the degradation in magnetic performance and failure from plastic deformation, but conventional SMMs (e.g., Fe–Co alloys and metallic glasses) struggle to surpass 1GPa in strength without sacrificing ductility or soft‐magnetic properties. Here, we pioneer a face‐centered cubic type Ni 40 Fe 30 Co 20 Al 10 multi‐principal element alloy (MPEA) engineered with a multi‐scale heterogeneous microstructure, achieving a nearly triple increase in yield strength (1103 MPa) while retaining 16% elongation and excellent soft‐magnetic response. This is realized through precipitation of coherent L1 2 nanoparticles (∼20 nm in diameter, ∼13 nm in spacing) during thermomechanical processing, which simultaneously impedes dislocation glide and minimizes domain wall pinning. Changes in magnetic exchange interaction and nanoparticle‐induced matrix magnetic moment slightly influence the saturation magnetic induction. Our strategy resolves the long‐standing trade‐off between mechanical robustness and soft‐magnetic performance, positioning such MPEAs as promising candidates for heavy‐load electromechanical systems.