Ferroelastic switching for nanoscale non-volatile magnetoelectric devices

Multiferroics, where (anti-) ferromagnetic, ferroelectric and ferroelastic order parameters coexist^1-5, enable manipulation of magnetic ordering by an electric field through switching of the electric polarization ^6-9. It has been shown that realization of magnetoelectric coupling in a single-phase multiferroic such as BiFeO₃ requires ferroelastic (71°, 109°) rather than ferroelectric (180°) domain switching ⁶. However, the control of such ferroelastic switching in a single-phase system has been a significant challenge as elastic interactions tend to destabilize small switched volumes, resulting in subsequent ferroelastic back-switching at zero electric field, and thus the disappearance of non-volatile information storage. Guided by our phase-field simulations, here we report an approach to stabilize ferroelastic switching by eliminating the stress-induced instability responsible for back-switching using isolated monodomain BiFeO₃ islands. This work demonstrates a critical step to control and use non-volatile magnetoelectric coupling at the nanoscale. Beyond magnetoelectric coupling, it provides a framework for exploring a route to control multiple order parameters coupled to ferroelastic order in other low-symmetry materials.