The effect of strain and strain symmetry on the charge-order transition in Bi0.4Ca0.6MnO3films

The transition to a charge and orbital ordered (CO/OO) state in epitaxial manganite films is strongly influenced by lattice strain. Bi1− x Ca x MnO3 is a particularly interesting material due to its high transition temperature and its relation to other Bi-based materials. Here, we review its properties and show the effects of strain and strain symmetry on Bi0.4Ca0.6MnO3 films on SrTiO3 (STO) and LaAlO3 substrates with (pseudocubic) (001) and (011) orientations. Transport and magnetization data are compared to four-circle X-ray diffraction and high-resolution Z-contrast scanning transmission microscopy data. We observe the spontaneous formation of single-unit-cell thick, Bi-rich layers only on (001) STO substrates and different defect structures depending on the substrate type and orientation. This shows that the details of epitaxial strain play a role not only at phase transitions, but also during the growth of these materials. Results are compared to those published for other CO/OO manganite films.