Interface-related phenomena in epitaxial complex oxide ferroics across different thin film platforms: opportunities and challenges

Interfaces in complex oxides give rise to fascinating new physical phenomena arising from the interconnected spin, lattice, charge and orbital degrees of freedom. Most commonly, interfaces are engineered in epitaxial superlattice films. Of growing interest also are epitaxial vertically aligned nanocomposite films where interfaces form by self-assembly. These two thin film forms offer different capabilities for materials tuning and have been explored largely separately from one another. Ferroics (ferroelectric, ferromagnetic, multiferroic) are among the most fascinating phenomena to be manipulated using interface effects. Hence, in this review we compare and contrast the ferroic properties that arise in these two different film forms, highlighting exemplary materials combinations which demonstrate novel, enhanced and/or emergent ferroic functionalities. We discuss the origins of the observed functionalities and propose where knowledge can be translated from one materials form to another, to potentially produce new functionalities. Finally, for the two different film forms we present a perspective on underexplored/emerging research directions.

Significant enhancement of energy storage density and polarization in self-assembled PbZrO3 : NiO nano-columnar composite films

Self-assembled nanostructures are important for determining the physical properties of epitaxial oxide films. We successfully fabricated perfectly ordered NiO nano-columns embedded in an antiferroelectric (AFE) PbZrO3 (PZO) matrix over large areas. In this system, a giant recoverable energy storage density of Wr = 24.6 J cm-3 and polarization of PS = 91 μC cm-2 were achieved in the structure of PZO : NiO nano-composites. These values are 333% and 253% larger than those of a pure PZO film, respectively. Additionally, the properties could be tuned by gradually changing the volume ratio of the constituents. Hence, we demonstrate a new approach for enhancing the energy storage of AFE materials and exercising control over nano-column-embedded nanocomposites.

Multiferroic nanocomposite fabrication via liquid phase using anodic alumina template

We report a novel and inexpensive fabrication process of multiferroic nanocomposite via liquid phase using an anodic alumina template. The sol-gel spin-coating technique was used to coat the template with ferrimagnetic CoFe₂O₄. By dissolving the template with NaOH aqueous solution, a unique nanotube array structure of CoFe₂O₄ was obtained. The CoFe₂O₄ nanotube arrays were filled with, and sandwiched in, ferroelectric BaTiO₃ layers by a sol-gel spin-coating method to obtain the composite. Its multiferroicity was confirmed by measuring the magnetic and dielectric hysteresis loops.