Training the Polarization in Integrated La0.15Bi0.85FeO3‐Based Devices

The functionalities of BiFeO3‐based magnetoelectric multiferroic heterostructures rely on the controlled manipulation of their ferroelectric domains and of the corresponding net in‐plane polarization, as this aspect guides the voltage‐controlled magnetic switching. Chemical substitution has emerged as a key to push the energy dissipation of the BiFeO3 into the attojoule range but appears to result in a disordered domain configuration. Using non‐invasive optical second‐harmonic generation on heavily La‐substituted BiFeO3 films, it is shown that a weak net in‐plane polarization remains imprinted in the pristine films despite the apparent domain disorder. It is found that this ingrained net in‐plane polarization can be trained with out‐of‐plane electric fields compatible with applications. Operando studies on capacitor heterostructures treated in this way show the full restoration of the domain configuration of pristine BiFeO3 along with a giant net in‐plane polarization enhancement. Thus, the experiments reveal a surprising robustness of the net in‐plane polarization of BiFeO3 against chemical modification, an important criterion in ongoing attempts to integrate magnetoelectric materials into energy‐efficient devices. A persisting net in‐plane polarization in highly La‐substituted multiferroic BiFeO3 films is probed operando using non‐invasive optical second‐harmonic generation directly in prototypical magnetoelectric device architectures. A spontaneous domain structure reordering triggered by the first electrical cycles leads to an abrupt enhancement of this net in‐plane polarization.