Single spin cycloid in multiferroic BiFeO₃ freestanding membranes

The spin cycloid characteristic of noncollinear antiferromagnets holds significant potential for energy-efficient, magnon-mediated spintronics. Multiferroic BiFeO₃ is one of the most promising candidates for such applications. However, epitaxial BiFeO₃ thin films grown on SrTiO₃ substrates (<200 nm) lose their spin-cycloid nature due to high compressive strain. Free-standing BiFeO₃ membranes, however, may restore the bulk-like spin cycloid even at much lower thicknesses. We successfully fabricated large-area (>5.0 mm²), single-ferroelastic, and ferroelectric domain BiFeO₃ free-standing membranes with thicknesses ranging from 50 to 1000 nm, with minimal cracks or wrinkles. Using Resonant Elastic X-ray Diffraction (REXS), we observed a single spin cycloid in membranes as thin as 100 nm. These bulk-like BiFeO₃ nanomembranes, with their robust single spin cycloid, offer a novel platform for ultra-low-energy magnonic device applications.