Affable thermal treatment process to overcome the trade-off relation via interface engineering in an Fe-based amorphous film

As pre-eminent soft magnetic materials, Fe-based amorphous alloys have been extensively studied due to adjustable composition, low cost, and low iron core loss. The soft magnetic properties could be further improved after thermal annealing, which achieve a low coercive force (Hc) due to the low magnetic anisotropy and a high saturation magnetic flux density (Bs) on account of the precipitation of soft magnetic nanocrystalline phases. However, it is a key difficulty to control the nucleation and growth procedures of nanocrystals during annealing, resulting in rapid deterioration of Hc. Here, a soft magnetic Fe76Si8B13Nb3 film with ultra-fine amorphous/crystalline (a/c) core–shell structure is achieved from an amorphous precursor with the nanoscale phase separation. The pre-existing nanoscale phase separation provides vast nucleation sites and interphase boundaries, which could generate high concentration of nanocrystals and depresses the subsequent coarsening behavior even for long-time heat treatment. In consequence, the a/c core–shell soft magnetic film breaks the general trade-off relation in the soft magnetic material family with the highest Bs and lowest Hc simultaneously. This work provides a new perspective to design a/c alloys by amorphous precursor with dual phase structure, and importantly, it supplies effortless thermal treatment requirement to conveniently regulate the microstructures and soft magnetic properties of metallic glasses.