Impersonating a Superconductor: High-Pressure BaCoO${}_3$, an Insulating Ferromagnet

Abstract

We report the high-pressure synthesis (6 GPa, 1200 ${}^{\circ }$C) and ambient pressure characterization of hexagonal HP-BaCoO${}_3$. The material (with the 2H crystal structure) has a short intrachain Co-Co distance of about 2.07 $\text{A˚}$. Our magnetization investigation revealed robust diamagnetic behavior below approximately 130 K when exposed to weak applied magnetic fields (10 Oe) and a distinct half-levitation phenomenon below that temperature, such 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) ${\mu }_B$/Co at a temperature of 2 K. Electrical resistivity measurements indicate that HP-BaCoO${}_3$ is a ferromagnetic insulator, not a superconductor.

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