Polarization Vector Canting in Croconic Acid Ferroelectric Nanoscopic Regions

Croconic acid is reported to be the organic ferroelectric with the highest above-room-temperature saturation polarization in its crystal form, at a value on par with that of commonly used inorganic ferroelectrics. Owing to its organic nature, high polarization value, and small coercive field, Croconic acid is considered as a potential candidate in energy-efficient and environmentally benign composite multiferroic heterostructures. However, understanding the magnetoelectric mechanism at the ferroelectric/ferromagnetic interface in these structures requires a detailed understanding of the orientation of the polarization vector in its thin film form. To maximize the magnetoelectric effect, the polarization vector should point out of the film plane, yet the polarization in ultra-thin Croconic acid films is predicted to lie in the film plane. Nevertheless, polycrystalline films show some promise in this direction. In this article, by combining in situ piezoreponse force microscopy imaging with nanoscopic polarization reversal spectroscopy, the authors qualitatively analyze the polarization switching and its orientation in polycrystalline Croconic acid films and show that it is canted with respect to the film plane, with a component along the out-of-plane direction.