(a) Timeline of selected milestones in BFO development. Progress in functionality (upper horizontal axis) is mapped against the evolution of characteristic structure sizes (vertical line). The transition from bulk crystals to thin films strengthened order-parameter couplings, reduced domain complexity, and added a weak ferromagnetic moment. Current device development, based on a nanoscale BFO/LSMO exchange bias bilayer, enables voltage control of the exchange bias field . (b) Graphical description of the voltage-controlled exchange bias effect. The LSMO exchange bias field (vertical dashed lines) shifts from a positive (left) to a negative (right) bias when a voltage is applied to the adjacent BFO layer.