Synergistic enhancement of permeability and reduction of core loss in FeNi50@SiO₂ soft magnetic composites via particle size tailored coating

Achieving both high permeability and low core loss in soft magnetic composites (SMCs) remains a critical challenge for high-frequency applications. This study demonstrates that this trade-off can be effectively overcome through particle size dependent interfacial engineering of the insulating coating. This study uncovers a previously overlooked intrinsic size effect, larger particles favor high permeability but inherently suffer from poor coating integrity due to their rough, grain boundary rich surfaces. Capitalizing on this finding, we propose a particle size dependent interfacial engineering strategy, wherein each size fraction is coated independently with a tailored precursor amount before recombination, thereby transforming the conventional uniform coating paradigm into a fraction wise architectural design. Different size fractions are coated with tailored amounts of precursor: larger particles receive more to form a thick, uniform layer, while smaller particles retain a thin coating. After recombining, a synergistic composite microstructure was constructed and the designed FeNi50@SiO 2 SMCs integrate the advantages of both fractions. This tailored approach yields a remarkable combination of soft magnetic properties: an effective permeability of 154.55 with an excellent frequency-stability and a core loss as low as 72.63 mW/cm 3 (50 kHz, 50 mT). These values represent a significant improvement of 13.25% in permeability and a reduction of 16.47% in loss compared to conventionally coated counterparts. Our work not only presents a superior FeNi50 based SMC but also establishes a generalizable microstructure design principle for advanced magnetic composites.