Designing rational particle grading is a pivotal strategy for developing high-performance soft magnetic composites (SMCs) for megahertz (MHz) electronic devices. Herein, FeNi SMCs with a dual-size system are fabricated by blending FeNi powders (median particle diameter, D₅₀ = 6 μm) with ultrafine FeNi powders (D₅₀ = 1 μm) at varying mass ratios. The microstructures and magnetic properties are found to be highly dependent on the content of ultrafine FeNi powders. Specifically, 10 wt.% ultrafine FeNi powders homogeneously fill the interstices between larger FeNi particles, resulting in improved tap density and crushing strength. Excessive addition of ultrafine FeNi powders, however, leads to reduced powder fluidity and particle aggregation, thereby deteriorating density. Owing to dense accumulation with a ratio of 9:1 between two powders, the enhanced density, effective permeability ( μ e of 65.4 at 1 MHz), and extremely low core loss ( P CV of 1032 mW/cm 3 at1 MHz/50 mT) can be realized simultaneously. Compared to ungraded FeNi SMC, the optimized composite exhibits a 14.8% increase in μ ₑ and an 8.6% reduction in P CV . Loss mechanism analysis revealed that reducing hysteresis loss, via mitigating demagnetizing field and dynamic coercivity, along with constructing high-quality insulation layers, holds significant potential for performance improvement. This work provides a facile strategy to produce high-frequency SMCs with desirable electromagnetic performance.
Wan et al. (Fri,) studied this question.