Searching for high magnetization density in bulk Fe: a new metastable Fe6 phase

Abstract:

We report the discovery of a new allotrope of bulk Fe by first principles calculations.

The new phase is characterized by a six-atom unit cell (hence the name Fe6) with a Pmn21 space group, and has the highest magnetization density among all known crystalline phases of bulk Fe. Although metastable under pressures ranging from 0 to 50 GPa, Fe6 is more stable than other well-known allotropes (hcp and fcc, in particular) at ambient conditions and continuously transforms into the FCC structure under compression. Having been obtained from the cementite structure of the Fe-C alloy, this phase could be stabilized by interstitial impurities and a possibility exists that the optimal stoichiometry is close to that of Fe16N2 whose high saturation magnetization density

(Ms) has not yet been fully understood. As starting material for high Ms rare-earth-free permament magnets, Fe6 could be used in high-impact applications as, e.g., new generation electric engine rotors or high-density recording media.