Lattice dynamics of BaFe₂Se₃

Area of Science:

• Condensed Matter Physics
• Materials Science
• Crystallography

Background:

• Barium Iron Selenide (BaFe2Se3) exhibits complex magnetic and structural properties.
• Previous studies suggested the Pnma space group, which is inconsistent with observed phenomena.

Purpose of the Study:

• To determine the correct space group of BaFe2Se3.
• To elucidate the relationship between lattice dynamics, spin order, and crystal structure.
• To provide a comprehensive symmetry analysis of the BaFe2Se3 phase diagram.

Main Methods:

• First-principle calculations were employed to model lattice dynamics.
• Infrared measurements provided experimental data on vibrational modes.
• A detailed symmetry analysis was performed to interpret structural and magnetic properties.

Main Results:

• The Pnma space group is definitively ruled out for BaFe2Se3, even at room temperature.
• The Pm space group is identified as the correct symmetry for both magnetic and paramagnetic phases.
• Strong spin-lattice coupling, driven by short-range spin order, alters Fe-Fe bond lengths, favoring a rectangular pattern over a trapezoidal one.

Conclusions:

• The Pm space group and the observed block-type magnetic structure are consistent.
• Spin-lattice coupling is a critical factor governing the structural phase of BaFe2Se3.
• A complete symmetry analysis of the BaFe2Se3 phase diagram from 0-600 K is proposed.