Emergent Antipolar Phase in BiFeO<sub>3</sub>-La<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub> Superlattice.

Dong, Wen; Peters, Jonathan J P; Rusu, Dorin; Staniforth, Michael; Brunier, Alan E; Lloyd-Hughes, James; Sanchez, Ana M; Alexe, Marin · Nano Lett · 2020

basic_science · Level V

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Abstract

Ferroelectric-paraelectric superlattices show emerging new states, such as polar vortices, through the interplay and different energy scales of various thermodynamic constraints. By introducing magnetic coupling at BiFeO<sub>3</sub>-La<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub> interfaces epitaxially grown on SrTiO<sub>3</sub> substrate, we find, for the first time in thin films, a sub-nanometer thick lamella-like BiFeO<sub>3</sub>. The emergent phase is characterized by an arrangement of a two unit cell thick lamella-like structure featuring antiparallel polarization, resulting an antiferroelectric-like structure typically associated with a morphotropic phase transition. The antipolar phase is embedded within a nominal <i>R</i>3<i>c</i> structure and is independent of the BiFeO<sub>3</sub> thickness (4-30 unit cells). Moreover, the superlattice structure with the morphotropic phase demonstrates azimuth-independent second harmonic generation responses, indicating a change of overall symmetry mediated by a delicate spatial distribution of the emergent phase. This work enriches the understanding of a metastable state manipulated by thermodynamic constraints by lattice strain and magnetic coupling.