Super-Flexible Freestanding BiMnO₃ Membranes with Stable Ferroelectricity and Ferromagnetism

Multiferroic materials with flexibility are expected to make great contributions to flexible electronic applications, such as sensors, memories, and wearable devices. In this work, super-flexible freestanding BiMnO₃ membranes with simultaneous ferroelectricity and ferromagnetism are synthesized using water-soluble Sr₃ Al₂ O₆ as the sacrificial buffer layer. The super-flexibility of BiMnO₃ membranes is demonstrated by undergoing an ≈180° folding during an in situ bending test, which is consistent with the results of first-principles calculations. The piezoelectric signal under a bending radius of ≈500 µm confirms the stable existence of electric polarization in freestanding BiMnO₃ membranes. Moreover, the stable ferromagnetism of freestanding BiMnO₃ membranes is demonstrated after 100 times bending cycles with a bending radius of ≈2 mm. 5.1% uniaxial tensile strain is achieved in freestanding BiMnO₃ membranes, and the piezoresponse force microscopy (PFM) phase retention behaviors confirm that the ferroelectricity of membranes can survive stably up to the strain of 1.7%. These super-flexible membranes with stable ferroelectricity and ferromagnetism pave ways to the realizations of multifunctional flexible electronics.