Impersonating a Superconductor: High-Pressure BaCoO₃, an Insulating Ferromagnet

Area of Science:

• Materials Science
• Solid State Physics
• Magnetism

Background:

• Hexagonal barium cobalt oxide (BaCoO3) is a material with potential for novel electronic and magnetic properties.
• Investigating high-pressure phases can reveal unique crystal structures and behaviors not accessible under ambient conditions.

Purpose of the Study:

• To synthesize and characterize hexagonal HP-BaCoO3 under high-pressure conditions.
• To elucidate the magnetic and electrical properties of this novel material.
• To determine if HP-BaCoO3 exhibits superconducting or ferromagnetic characteristics.

Main Methods:

• High-pressure synthesis at 6 GPa and 1200 °C.
• Ambient-pressure characterization including magnetization and electrical resistivity measurements.
• Analysis of crystal structure and magnetic properties.

Main Results:

• Successful synthesis of hexagonal HP-BaCoO3 with a 2H crystal structure.
• Observed diamagnetic behavior and a "half-levitation" phenomenon below 130 K, mimicking some superconducting traits.
• Magnetization measurements revealed ferromagnetic characteristics with significant retentivity (0.22(1) μB/Co at 2 K).
• Electrical resistivity confirmed the material is an insulator.

Conclusions:

• Hexagonal HP-BaCoO3 is a ferromagnetic insulator, not a superconductor.
• The observed diamagnetic behavior and half-levitation are distinct from its underlying ferromagnetic nature.
• High-pressure synthesis is a viable route to explore novel material properties.