Magnetic Hardening in Fe-based Carbides

Magnetic coercivity is the most important property for permanent magnet applications. In conventional permanent magnets, high coercivity originates from magnetocrystalline anisotropy that can be found from ferromagnetic compounds containing heavy elements, like rare earths. However, rare-earth elements used for permanent magnets are now considered as critical materials for the supply chain and environmental issues. It is therefore essential to search hard magnetic materials based on earth abundant elements like Fe. We have successfully prepared Fe₅C₂ nanocrystals that have a high coercive field of 1.9 kOe at room temperature, which is the record high value for this material to date. The nanocrystals with monoclinic crystal structure (C2/c space group) were synthesized using a chemical solution approach. The samples contain nanoparticles and nanorods, with a diameter of about 20-30 nm and a length of 60-90 nm. The magnetic measurements also show that the Fe₅C₂ phase exhibits saturation magnetization of ~122 emu/g. Thermal magnetic measurement reveals that the Curie temperature of Fe₅C₂ is ~ 520 K, which is highly suitable for permanent magnet application at room temperature and above.

Reference:

1. Jeotikanta Mohapatra, X. Liu, P. Joshi, J. Ping Liu, Hard and Semi-hard Fe-based Magnetic Materials, J. of Alloys and Compounds, Volume 955, 10 September 2023, 170258.