In situ synthesis of Hägg iron carbide (Fe5C2) nanoparticles with a high coercivity and saturation magnetization

Magnetic nanoparticles (NPs) suffer from poor magnetic properties (coercivity and saturation magnetization) compare to their bulk. Synthesis of Hägg iron carbide, Fe5C2 magnetic nanoparticles (NPs) was still a challenge for the pure phase and the large-scale production. Herein, a chemical solution route was proposed to obtain pure Fe5C2 phase using amorphous Fe NPs as iron feedstock in presence of Oleylamine (OAm) at elevated temperature. X-ray diffraction results reveal the pure Hägg iron carbide phase for various reaction time from 30 min to 9 h. Fe5C2 NPs show the same morphology as Fe NPs by scanning electron microscopy (SEM) and transmission electron microscope (TEM). Amorphous Fe NPs catalyze the cleavage of C–C bonds of OAm at elevated temperature as well act as a template for the in situ nucleation and growth of Fe5C2 NPs. The saturation magnetization of Fe5C2 NPs are 140 emu/g and 123 emu/g for 5 K and 298 K, respectively. The coercive force of Fe5C2 NPs are 452 Oe (298 K) and 703 Oe (5 K), demonstrating the ferromagnetic behavior. The magnetic Fe5C2 NPs showed the high coercivity and saturation magnetization on the nanoscale, revealing the Fe5C2 NPs being a promise candidate for the soft magnetic application such as magnetic medium. This paper presents a convenient procedure to synthesize Hägg iron carbide nanoparticles and may promote its further study in formation mechanism and application such as catalysis.