The Balance Between Low Core Loss, High Permeability, and Large DC Bias Performance in FeSiAl Cores Covered by Polydopamine/Polyethyleneimine

The balance low core loss (P_cv), high permeability (μ_e), and large DC bias requires a good insulation effect and weak pinning on the magnetic moment of insulating layers. In this work, due to lightweight, integrity, and a special bonding method, polydopanmine (PDA)/polyethyleneimine (PEI) layers are adopted to cover FeSiAl powder through a chelation process. The PDA/PEI layer undergoes an evolution process from coating, density, and crack occurrence to fracture at 500–800 °C. P_cv values rapidly decrease as the annealing temperature increases from 500 °C to 700 °C, due to the decrease of hysteresis loss (P_h) induced by stress elimination. At 800 °C, P_cv values slightly deteriorate because the destruction of the insulating layer leads to a significant increase in eddy-current loss (P_e). The integrity of the thin insulating layer ensures a good insulation effect among FeSiAl powders, resulting in low P_cv. The lightweight double organic layers alleviate dilute magnetism and weakly pin on the surface magnetic moment rotation, leading to high μ_e. FeSiAl cores, which are covered by 12 mg/mL PDA/PEI and annealed at 700 °C, have good comprehensive performances with a μ_e of 53.2 until 1000 kHz and 140 °C, P_cv of 63.8 mW/cm³ (100 kHz/50 mT) and 341 mW/cm³ (100 kHz/100 mT), and a DC bias of 50.9% at 100 Oe. This work highlights a new strategy for fabricating high-performance kinds of soft magnetic composite (SMC) applications in inductors.