Direct observation of ferroelectricity in Ca3Mn2O7 and its prominent light absorption.

Layered perovskites <italic>A</italic>3<italic>M</italic>2O7 are known to exhibit the so-called hybrid improper ferroelectricity. Despite experimentally confirmed cases (e.g., nonmagnetic <italic>M</italic> = Ti and Sn), the ferroelectricity in magnetic Ca3Mn2O7 remains a puzzle. Here, the structural, ferroelectric, magnetoelectric, and optical properties of Ca3Mn2O7 are systematically investigated. Switchable polarization is directly measured, demonstrating its ferroelectricity. In addition, magnetoelectric response is also evidenced, implying the coupling between magnetism and ferroelectricity. Furthermore, strong visible light absorption is observed, which can be understood from its electronic structure. Its direct and appropriate bandgap, as well as wide conducting bands, makes Ca3Mn2O7 a potential candidate for ferroelectric photoelectric applications. [ABSTRACT FROM AUTHOR]