Highly Flexible Freestanding BaTiO₃-CoFe₂O₄ Heteroepitaxial Nanostructure Self-Assembled with Room-Temperature Multiferroicity

Multiferroics with simultaneous electric and magnetic orderings are highly desirable for sensing, actuation, data storage, and bio-inspired systems, yet developing flexible materials with robust multiferroic properties at room temperature is a long-term challenge. Utilizing water-soluble Sr₃Al₂O₆ as a sacrificial layer, the authors have successfully self-assembled a freestanding BaTiO₃-CoFe₂O₄ heteroepitaxial nanostructure via pulse laser deposition, and confirmed its epitaxial growth in both out-of-plane and in-plane directions, with highly ordered CoFe₂O₄ nanopillars embedded in a single crystalline BaTiO₃ matrix free of substrate constraint. The freestanding nanostructure enjoys super flexibility and mechanical integrity, not only capable of spontaneously curving into a roll, but can also be bent with a radius as small as 4.23 µm. Moreover, piezoelectricity and ferromagnetism are demonstrated at both microscopic and macroscopic scales, confirming its robust multiferroicity at room temperature. This work establishes an effective route for flexible multiferroic materials, which have the potential for various practical applications.