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

We report the high-pressure synthesis (6 GPa, 1200 °C) and ambient-pressure characterization of hexagonal HP-BaCoO₃. The material (with a 2H crystal structure) has a short intrachain Co-Co distance of about 2.07 Å. Our magnetization investigation revealed robust diamagnetic behavior below approximately 130 K when the material was exposed to weak applied magnetic fields (10 Oe) and a distinct “half-levitation” phenomenon below that temperature, as is often observed for superconductors. Its field-dependent magnetization profile, however, unveils the characteristics of ferromagnetism, marked by a substantial magnetic retentivity of 0.22(1) μ_B/Co at a temperature of 2 K. Electrical resistivity measurements indicate that HP-BaCoO₃ is a ferromagnetic insulator, not a superconductor.