Bi 2 CoO 2 F 4 -A Polar, Ferrimagnetic Aurivillius Oxide-Fluoride.

Aurivillius oxides have been a research focus due to their ferroelectric properties, but by replacing oxide ions by fluoride, divalent magnetic cations can be introduced, giving Bi OF ( = Fe, Co, and Ni). Our combined experimental and computational study on BiCoOF indicates a low-temperature polar structure of 2 symmetry (analogous to ferroelectric BiWO) and a ferrimagnetic ground state. These results highlight the potential of Aurivillius oxide-fluorides for multiferroic properties. Our research has also revealed some challenges associated with the reduced tendency for polar displacements in the more ionic fluoride-based systems.