Boosted Nanocrystalline Magnetic Softness via Atomic Immiscibility Induced Chemical Heterogeneity

Abstract Soft magnetic nanocrystalline alloys are technically crucial in power electronics, whereas confront the traded‐off between high saturation magnetic flux density ( B _s ) and low coercivity ( H _c ) due to the incorporation of non‐magnetic elements or harsh crystallization process. To tackle this challenge, deep supercooling solidification and strong immiscibility system are employed to prepare Fe ₈₆ Si _1.3 B ₉ C ₂ Cu _1.7 nanocrystalline alloy with superior magnetic softness. Benefitting from synergistically enhanced glass‐forming ability (GFA) and atomic immiscibility, grain nucleation is thermodynamically promoted with the formation of dense Cu‐rich clusters and Fe‐rich regions. Such localized chemical heterogeneity induces significant elemental gradients between the amorphous matrix and growing grains, resulting in enhanced competitive growth and decreased grain size. Dynamic magnetization and micromagnetic simulations reveal that the dense and fine nanocrystalline microstructure contributes to smooth domain motion as well as reduced magnetic anisotropy energy and exchange energy, giving rise to exceptional magnetic properties ( B _s = 1.90 T, H _c = 4.0 A m ⁻¹ ). As such, this study not only unveils chemical heterogeneity to enhance soft magnetic properties of nanocrystalline alloys but also provides a novel strategy for tailoring the microstructure of amorphous/nanocrystalline alloys to improve electrical, mechanical, and catalytic properties.