Flexible Multiferroic Heterostructure Based on Freestanding Single‐Crystalline BaTiO3 Membranes for Spintronic Devices

Abstract One of the key concepts in flexible/freestanding spintronics is the effective control of ultra‐thin film magnetism, and at the same time assures that the functional properties will not be compromised when gating methods are applied. Traditionally, strain application is through magnetoelectric effect while using the gate voltage to transfer the strain to the magnetism layer, which can lead the noise in the heterostructure. On the other hand, the knowledge of freestanding magnetism changes largely lacks quantitative analysis. Coupling the freestanding characteristic such as large strain with important magnetic properties can further expand the freestanding spintronics storage area. In this work, the high‐quality freestanding multiferroic heterostructures of SrTiO 3 (001)/Sr 3 Al 2 O 6 /BaTiO 3 /Ta/(Co/Pt) 5 with different Co thicknesses have been successfully prepared with both pulsed laser deposition and magnetism sputtering processes. The ultra‐flexible freestanding structure shows a strong strain gating effect with bending, that the ferromagnetic resonance (FMR) shifts around 440 Oe at room temperature with tensile strain. Upon decreasing the temperature to BaTiO 3 phase transition range from T‐phase to O‐phase and O‐phase to R‐phase, respectively, a sharp FMR shift can be observed for both in‐plane and out‐of‐plane measurements. This work suggests that the tunable flexible spintronics are achievable through freestanding mechanisms and shows the promising future of freestanding spintronics.