Tetragonal distortion of the multiferroic compound α-LiFe₅O₈ from first-principles calculations

Area of Science:

• Condensed Matter Physics
• Materials Science
• Crystallography

Background:

• Previous studies reported a cubic space group (P4332) for multiferroic lithium ferrite (α-LiFe5O8, LFO).
• The precise crystallographic and magnetic structure of LFO's ground state requires further investigation for accurate property prediction.

Purpose of the Study:

• To determine the accurate ground state crystal structure of multiferroic lithium ferrite (LFO).
• To investigate the electronic and magnetic properties of LFO using first-principles calculations.

Main Methods:

• Utilized PBEsol+U calculations with SSSP pseudopotentials for accurate electronic structure determination.
• Performed spin-resolved projected density of states analysis to understand electron localization.
• Analyzed magnetic space groups and superexchange interactions to explain structural properties.

Main Results:

• Identified the tetragonal space group P43212 as the true ground state for LFO, challenging previous cubic assignments.
• Calculated a direct band gap of 2.050 eV for the tetragonal LFO, with strong Fe3+ 3d electron localization.
• Observed a ferrimagnetic ground state with collinear spin order along the c-axis, consistent with group theory predictions.

Conclusions:

• The tetragonal structure of LFO arises from competing ferromagnetic and antiferromagnetic interactions along the c-axis.
• Strong Fe-O-Fe superexchange interactions are key drivers of the observed tetragonal lattice distortion in LFO.
• This study provides a refined structural and electronic model for multiferroic lithium ferrite.