Deterministic and robust room-temperature exchange coupling in monodomain multiferroic BiFeO₃ heterostructures

Exploiting multiferroic BiFeO₃ thin films in spintronic devices requires deterministic and robust control of both internal magnetoelectric coupling in BiFeO₃, as well as exchange coupling of its antiferromagnetic order to a ferromagnetic overlayer. Previous reports utilized approaches based on multi-step ferroelectric switching with multiple ferroelectric domains. Because domain walls can be responsible for fatigue, contain localized charges intrinsically or via defects, and present problems for device reproducibility and scaling, an alternative approach using a monodomain magnetoelectric state with single-step switching is desirable. Here we demonstrate room temperature, deterministic and robust, exchange coupling between monodomain BiFeO₃ films and Co overlayer that is intrinsic (i.e., not dependent on domain walls). Direct coupling between BiFeO₃ antiferromagnetic order and Co magnetization is observed, with ~ 90° in-plane Co moment rotation upon single-step switching that is reproducible for hundreds of cycles. This has important consequences for practical, low power non-volatile magnetoelectric devices utilizing BiFeO₃.