Fe@SiO2@(MnZn)Fe2O4 soft magnetic composites with enhanced permeability and low core loss for high-frequency applications

Abstract

Novel core-shell-shell Fe@SiO2@(MnZn)Fe2O4 soft magnetic composites (SMCs) with low core loss and high permeability were fabricated by a facile continuous chemical co-precipitation route and subsequent powder metallurgy technique. The typical double-shell structure for Fe@SiO2@(MnZn)Fe2O4 powders was composed of a SiO2−(MnZn)Fe2O4 mixed outer layer and an SiO2 inner network embedded with trace amounts of (MnZn)Fe2O4. In comparison with Fe@SiO2 SMCs, the Fe@SiO2@(MnZn)Fe2O4 SMCs presented a notable flat high frequency characteristic up to 1 MHz, much higher permeability, and lower core loss which reduced with decreasing (MnZn)Fe2O4 layer thickness. Fe@SiO2@(MnZn)Fe2O4 SMCs prepared with 4 mL (MnZn)Fe2O4 solution exhibited stable permeability of 64.0–63.5 up to 1 MHz and low core loss of 0.9–30.6 W/kg in 1–150 kHz. The strong magnetic coupling between the thin (MnZn)Fe2O4 layer and Fe cores effectively reduced the air-gap thickness and demagnetization field giving rise to a high permeability. The low core loss could be attributed to the full separation of Fe core by thin dielectric−electrically insulating magnetic coupled with a SiO2/(MnZn)Fe2O4 insulating layer. Our findings might shed insight on the design of novel SMCs with low core loss and high permeability.