BFO can suffer loss of functionality below ten unit cells.

The loss of both antiferromagnetism and switchable polarization in BiFeO3 (BFO) at thicknesses below ten unit cells presents a significant hurdle for microelectronic device scaling. Researchers report this double-failure mode stems primarily from strong depolarizing electric fields inherent to BFO’s large out-of-plane ferroelectric polarization. Similar magnetic dead layers are already well-known in manganites, suggesting a broader issue with functionality loss in correlated thin films. This work demonstrates an atomic-scale design strategy to stabilize both ferroelectric and magnetic order in BFO, even at thicknesses less than three nanometers, and probe emergent coupled polar-magnetic phases. This stabilization relies on inducing compressive strain through lattice mismatch between the BFO film and its substrate, coupled with electronic screening from a lattice-matched oxide electrode. To suppress the depolarizing electric fields that typically cause the loss of both magnetism and switchable polarization, the team synthesized BFO on a lattice-matched oxide electrode. Large epitaxial compressive strain was then imposed using a lattice-mismatched substrate to stabilize out-of-plane structural distortions, and consequently, out-of-plane polarization. Reactive oxide molecular-beam…