Emergent Uniaxial Magnetic Anisotropy in High-Integrity, Uniform Freestanding LaMnO Membranes.

The water-liftoff fabrication of freestanding oxide membranes at nanometer-scale thickness marks a major breakthrough in expanding the family of soft electromagnetic materials. The structure reconstruction in the newly formed two-dimensional freestanding membrane due to the chemical liftoff provides an excellent opportunity to achieve applicable functionalities. In this report, we present the anisotropic relaxation of a LaMnO epitaxial film into a nearly wrinkle- and crack-free membrane, realized by high-temperature (160 °C)-treated PMMA as the protective layer during the water liftoff process. Remarkably, the resulting membrane exhibits a 2-fold uniaxial magnetic anisotropy, which is in stark contrast to the typical 4-fold biaxial magnetic anisotropy in biaxially strained epitaxial thin films. By performing half-order synchrotron X-ray diffraction experiments, the membrane is found to exhibit almost unvaried Mn-O bond lengths but uniaxially enlarged Mn-O-Mn bond angles, agreeing with the uniaxial magnetic anisotropy. Our study paves the way for engineering macroscopically high-quality membranes free of wrinkles and cracks, unlocking emergent electromagnetic properties that are essential for the integration and application of functional devices.