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

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• Iron exhibits various allotropes (crystal structures) with distinct properties.
• Understanding iron's phase behavior is crucial for materials science and technological applications.
• Existing iron allotropes have limitations in magnetic properties and stability.

Purpose of the Study:

• To report the discovery of a novel iron allotrope.
• To characterize its structural and magnetic properties.
• To explore its potential applications.

Main Methods:

• First principles calculations were employed for discovery and characterization.
• Structural optimizations were performed on Fe3C-cementite.
• Analysis of phase stability across a pressure range (0-50 GPa).

Main Results:

• A new iron allotrope, designated Fe6, with Pmn2(1) symmetry and a six-atom unit cell was identified.
• Fe6 exhibits the highest known magnetization density (Ms) among crystalline iron phases.
• This metastable phase is more stable than HCP and FCC iron at low pressures and transforms to FCC under compression.

Conclusions:

• Fe6 represents a significant discovery in iron allotropes.
• Its high Ms suggests potential for rare-earth-free permanent magnets.
• Stabilization of Fe6 could lead to applications in electric engines and data storage.