A rigorous investigation of BiMnO3 ferroelectricity through a development of a novel way to stabilize twin free and monoclinic thin film

Bulk BiMnO3 has a monoclinic structure and exhibits ferromagnetic properties below Tc similar to 105 K. The existence of ferroelectricity was one of the hottest issues in this compound. To investigate the ferroelectricity in BiMnO3, a good film with low-enough leakage is highly required. However the reported quality of BiMnO3 thin films has shown critical dependence on stoichiometry. Previously, we reported that a BiMnO3 thin film grown on top of a SrTiO3 (001) substrate has good stoichiometry, as well as bulk-quality ferromagnetic properties, but our results did not demonstrate the Q-E hysteresis curves. However, we could not exclude the possibility that non-ferroelectricity observed in the BiMnO3 film is partly due to the tetragonal symmetry enforced by the strong epitaxial strain of the substrate since the ferroicity in most oxides accompanies with or equivalently originates from crystal symmetry breaking and/or lowering. In the present work, we used a SrTiO3 (110) substrate with an anisotropic in-plane atomic arrangement to stabilize the BiMnO3 thin film having the symmetry lower than tetragonal symmetry. After observing the stabilization of twined monoclinic phase in the BiMnO3 film, we solved the twin problem by trying a novel substrate; i.e., miscut SrTiO3 (110) substrate. The physical properties for the stoichiometric, twin-free, monoclinic BiMnO3 thin film were notably similar to those reported for the stoichiometric BiMnO3 bulk with monoclinic symmetry. We believe this new data more rigorously demonstrates the absence of ferroelectricity in stoichiometric monoclinic BiMnO3. (C) 2016 Elsevier B.V. All rights reserved.