Robust Ferroelectric Properties Of Organic Croconic Acid Films Grown On Spintronically Relevant Substrates

The discovery of stable room temperature ferroelectricity in croconic acid, an organic ferroelectric material, with polarization values on par with those found in inorganic ferroelectric materials and highest among organic ferroelectric materials, has opened up possibilities to realize myriads of nano-electronic and spintronic devices based on organic ferroelectrics. Such possibilities require an adequate understanding of the ferroelectric properties of croconic acid grown on surfaces that are commonly employed in device fabrication. While several macroscopic studies on relatively larger crystals of croconic acid have been performed, studies on thin films are only in their early stages. We have grown thin films of croconic acid on gold and cobalt surfaces, which are commonly used in spintronic devices as metallic electrodes, and studied the films' ferroelectric response using ex situ piezoresponse force microscopy at room temperature. We show that the polarization reversal in croconic acid domains is sensitive to the substrate surface. Using the same experimental protocol, we observe the robust polarization reversal of a single, mostly in-plane electrical domain for a cobalt substrate, whereas polarization reversal is hardly observed for a gold substrate. We attribute this difference to the substrate's influence on the croconic acid molecular networks. Our study suggests that to realize devices one has to take care about the substrate on which croconic acid will be deposited. The fact that polarization switching is robust on the cobalt surface can be used to fabricate multifunctional devices that utilize the cobalt/croconic acid interface.