Hydride-Reduced Eu₂SrFe₂O₆: A T-to-T' Conversion Enabling Fe²⁺ in Square-Planar Coordination

Area of Science:

• Materials Science
• Solid-State Chemistry
• Magnetism

Background:

• Layered perovskites are a class of materials with diverse electronic and magnetic properties.
• The T' structure is known for specific cation arrangements and associated properties.
• Understanding cation reduction and its impact on crystal structure and magnetism is crucial.

Purpose of the Study:

• To synthesize and characterize a novel T'-structure layered perovskite, Eu2SrFe2O6.
• To investigate the role of Fe cation reduction in stabilizing the T' structure.
• To explore the magnetic properties and electronic structure of the synthesized material.

Main Methods:

• Low-temperature synthesis using calcium hydride (CaH2) on A-site-ordered layered perovskite Eu2SrFe2O7.
• X-ray diffraction and density functional theory (DFT) calculations for structural and electronic analysis.
• Magnetic susceptibility measurements to determine magnetic ordering temperature (Néel temperature, TN).

Main Results:

• Successful synthesis of Eu2SrFe2O6 with a T' structure (I4/mmm space group) via low-temperature reaction.
• Stabilization of the T' structure is attributed to the Fe2+ (d6) cation and the FeO4 square-planar unit.
• DFT calculations confirmed the stability of the T' structure and revealed d-orbital occupancy.
• Eu2SrFe2O6 exhibits a bilayer magnetic framework with Fe-O-Fe superexchange (J∥) and direct Fe-Fe exchange (J⊥), with J∥ > J⊥.
• Observed Néel temperature (TN) ranges from 390-404 K, consistent with the magnetic framework.
• Magnetic moments align in the ab plane, differing from related compounds with out-of-plane alignment.

Conclusions:

• The study demonstrates the successful synthesis of a novel T'-structure layered perovskite, Eu2SrFe2O6.
• The FeO4 square-planar unit plays a key role in stabilizing this structure with Fe2+ cations.
• The material's magnetic properties are governed by a bilayer framework with in-plane spin alignment and a high Néel temperature.