Super‐Flexible Freestanding BiMnO₃ Membranes with Stable Ferroelectricity and Ferromagnetism

Abstract

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 BiMnO 3 membranes with simultaneous ferroelectricity and ferromagnetism are synthesized using water-soluble Sr 3 Al 2 O 6 as the sacrificial buffer layer. The super-flexibility of BiMnO 3 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 BiMnO 3 membranes. Moreover, the stable ferromagnetism of freestanding BiMnO 3 membranes is demonstrated after 100 times bending cycles with a bending radius of ≈2 mm. 5.1% uniaxial tensile strain is achieved in freestanding BiMnO 3 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.

Freestanding Perovskite Oxide Films: Synthesis, Challenges, and Properties

“…[84] Many polymer materials have been developed and used as support layers, considering the merits of flexibility, mechanical strength, and adhesive contact, such as polyimide (PI) tape, polydimethylsiloxane (PDMS), [11,12,82,87] polymethyl-methacrylate (PMMA), [20,62] polystyrene (PS), or the combination of these materials, like polypropylene carbonate (PPC)-PDMS stack [13,62,87] and PI sheet with PPC layer. [52,67] PMMA, which is most commonly used in transferring of chemical-vapor-deposited graphene, [38,84] has also found a wide application in the transfer of oxide membrane. [20,62,42] PMMA can be easily coated on the oxide surface, and washed away by acetone once the transfer is completed, see Figure 3a.…”

“…[22,30] Indeed, it was shown that single-crystal perovskite membranes can sustain extremely large tensile strain before breaking. [22,69,30,35,38,122] In particular, Harbola et al showed that in single-crystal membranes of STO the tensile strain strength can be as high as 6%, almost an order of magnitude more than in bulk form. [22] A nonmonotonic change of the Young modulus in nanometric membranes of STO was also observed, due to a competitive behavior of surface elasticity and strain gradient elasticity.…”

“…[23] Moreover, ferroelectric freestanding perovskite thin films display superelasticity and ultraflexibility at the nanoscale, due to a continuous rotation of the polarization direction and to local phase transformations that avoid mechanical failure. [69,30,35,38,122] More details about this phenomenon and about the effects of strain in freestanding perovskite oxides will be discussed in Section 4 of this work.…”

“…As commented in Section 3.2, the study of ferroelectric self-sustained membranes subjected to large bending strain showed that these ceramic materials, generally considered brittle in bulk, possesses superelasticity and ultraflexibility at the nanoscale. [69,30,35,38,122] Dong et al first showed that single-crystalline ferroelectric BTO membrane can withstand an remarkable tensile strain of 10% without breaking. [30] The origin of this superelasticity was found to lie in a continuous rotation of the polarization direction in BTO membranes, which efficiently avoid mismatch stress and delay the membrane failure.…”

“…As commented in Section 3.3, it was shown that freestanding perovskite thin films can withstand extremely large tensile strain before breaking, allowing the investigation of strain states not achievable in bulk and substrate-supported perovskite oxides. [22,23,69,30,35,38,122] The mechanical stretching method was first used by Hong et al to study the magnetotransport properties of T c ) measured in STO membranes as a function of uniaxial strain and predicted by numerical models. Reproduced under terms of the CC-BY license.…”