Atomic-scale engineering of ferroelectric-ferromagnetic interfaces of epitaxial perovskite films for functional properties

• Published in: Scientific reports 2017-09, Vol.7 (1), p.10734-16, Article 10734
• Main Authors: Hausmann, Simon, Ye, Jingfan, Aoki, Toshihiro, Zheng, Jian-Guo, Stahn, Jochen, Bern, Francis, Chen, Binda, Autieri, Carmine, Sanyal, Biplab, Esquinazi, Pablo D., Böni, Peter, Paul, Amitesh
• Format: Article
• Language: English
• Subjects: 639/301/357; 639/925/357; Electron microscopy; Humanities and Social Sciences; Interfaces; multidisciplinary; Physical properties; Science; Science (multidisciplinary); Symmetry; Transmission electron microscopy
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-017-10194-4

Besides epitaxial mismatch that can be accommodated by lattice distortions and/or octahedral rotations, ferroelectric-ferromagnetic interfaces are affected by symmetry mismatch and subsequent magnetic ordering. Here, we have investigated La 0.67 Sr 0.33 MnO 3 (LSMO) samples with varying underlying unit cells (uc) of BaTiO 3 (BTO) layer on (001) and (110) oriented substrates in order to elucidate the role of symmetry mismatch. Lattice mismatch for 3 uc of BTO and symmetry mismatch for 10 uc of BTO, both associated with local MnO 6 octahedral distortions of the (001) LSMO within the first few uc, are revealed by scanning transmission electron microscopy. Interestingly, we find exchange bias along the in-plane [110]/[100] directions only for the (001) oriented samples. Polarized neutron reflectivity measurements confirm the existence of a layer with zero net moment only within (001) oriented samples. First principle density functional calculations show that even though the bulk ground state of LSMO is ferromagnetic, a large lattice constant together with an excess of La can stabilize an antiferromagnetic LaMnO 3 -type phase at the interface region and explain the experimentally observed exchange bias. Atomic scale tuning of MnO 6 octahedra can thus be made possible via symmetry mismatch at heteroepitaxial interfaces. This aspect can act as a vital parameter for structure-driven control of physical properties.