Magneto-structural transformations via a solid-state nudged elastic band method: Application to iron under pressure

Area of Science:

• Solid-state physics
• Materials science
• Computational materials science

Background:

• Magneto-volume effects are crucial in magnetic systems.
• Pressure-induced phase transitions in iron are well-studied but complex.
• Understanding magnetization coupling to volume is essential for magnetic materials.

Purpose of the Study:

• To extend the nudged elastic band method for non-conserved order parameters like magnetization.
• To investigate the magneto-volume collapse in iron during the austenite to martensite transformation.
• To accurately model the pressure-induced phase transition in iron.

Main Methods:

• Solid-state nudged elastic band method
• Incorporation of non-conserved order parameter (magnetization)
• First-principles calculations

Main Results:

• Calculated an equilibrium coexistence pressure of 8.4 GPa for the bcc-hcp transition in iron.
• Determined a transition-state enthalpy of 156 meV/Fe at 8.4 GPa.
• Observed a discontinuity in magnetization and coherent stress at the transition state, with a calculated pressure jump of 25 GPa.

Conclusions:

• The extended method accurately models magneto-volume effects in iron.
• Results align with experimental observations of pressure-induced transitions and stress.
• The approach provides a more robust framework compared to previous methods with constrained degrees of freedom.