Chemical synthesis of Fe/Fe₃O₄ core-shell composites with enhanced soft magnetic performances

The large-grain Fe/Fe₃O₄ composite particles with average size of about 1.2 µm have been fabricated by a facile one-step solvothermal method. The formation of high-purity Fe₃O₄ as the shells (90.14 wt%) and α-Fe as the cores (9.86 wt%) in the Fe/Fe₃O₄ composites leads to their high saturation magnetization of 119.6 A m² Kg^-1. Very low coercivity of 30 Oe is obtained in the composites due to their uniform cubic-shaped morphologies. Compared with Fe-based nanosized particles, these micron-sized magnetic Fe/Fe₃O₄ composites exhibit high air stability and good compactibility with high compressed density of 5.9 g cm^-3. The fully compacted sample shows good soft magnetic properties including high magnetic induction B_{1.2k (H=1200 A/m)} of 540 mT and good frequency-dependent magnetic properties with operating frequency up to 50 MHz superior to those of the most traditional soft magnetic ferrites, which promotes their potential applications in high-frequency and high-power magnetic devices.