Review of magnetoelectric perovskite–spinel self-assembled nano-composite thin films

Two-phase multiferroic nano-composite thin films have been a topic of research interests in the last few years. This is because of their expected magnetoelectric coupling, as well as potential applications. This review focuses on recent findings in self-assembled nano-structure composite thin films, and various efforts to realize and improve their magnetoelectricity. Topics include: (i) nano-pillar and maze structures, and their formation mechanisms, and a nano-belt structure oriented in-plane found by our research group; (ii) the ferroelectric properties of composite thin films, and how they can be enhanced by epitaxial engineering; (iii) a magnetic anisotropy that is induced by constraint stress, and by the nano-structures of the ferromagnetic phase; and (iv) a magnetoelectric coupling that was first observed via a change in magnetization near the Curie temperature of the ferroelectric phase, a magnetization switching assisted by electric field, and recently direct measurements using a magnetic cantilever method yielding values of 18 mV/cm Oe in BiFeO3–CoFe2O4.