Bulk‐Like Spin Cycloid and Fast Switching in Freestanding BiFeO 3

ABSTRACT The spin cycloid characteristic of noncollinear antiferromagnets offers significant potential for energy‐efficient, magnon‐mediated spintronic applications. Multiferroic BiFeO 3 is among the most promising candidate materials because its antiferromagnetic order can be controlled by an electric field. However, in epitaxial BiFeO 3 thin films, substrate clamping and epitaxial strain modify the cycloidal magnetic structure while limiting efficient ferroelastic‐ferroelectric switching. Here, we show that strain‐released freestanding BiFeO 3 membranes overcome these limitations. Compared with substrate‐clamped epitaxial thin films, a 100‐nm‐thick freestanding membrane exhibits ≈50% faster electric‐field‐driven ferroelectric switching and a spatially uniform, bulk‐like single spin cycloid, as revealed by resonant elastic X‐ray scattering. In contrast, the epitaxial thin film exhibits an expanded cycloid periodicity and slower ferroelectric switching dynamics, reflecting the influence of substrate‐induced strain. Freestanding BiFeO 3 membranes therefore overcome substrate‐induced constraints by simultaneously restoring the intrinsic bulk‐like spin cycloid and enabling substantially faster ferroelectric switching. This combination of robust noncollinear antiferromagnetic order and efficient electric‐field switching establishes freestanding BiFeO 3 membranes as a promising magnetoelectric platform for low‐power magnonic and spintronic technologies, while enabling heterogeneous integration with Si‐based devices.