Relationship between structure and charge/orbital order in epitaxial single layer Ruddlesden–Popper manganite thin films

Ruddlesden–Popper manganites are strongly correlated, quasi two-dimensional systems with highly tunable functional properties, which can, for example, be controlled by composition, strain, and defects. Praseodymium calcium manganite is a particularly interesting Ruddlesden–Popper system due to its remarkably high temperature at which ordering phenomena set in, enabling correlation physics above room temperature. However, in order to utilize the correlation phenomena and the quasi-two-dimensionality of the Ruddlesden–Popper systems for applications, one needs to grow thin film junctions, making it necessary to control the structure–property relation of Ruddlesden–Popper thin films. Here, we present a cryogenic transmission electron microscopy study of praseodymium calcium manganite thin films, deposited on niobium doped strontium titanate substrates, where we analyze the structure of the manganite thin film, as well as the effect of the epitaxial strain and defects on the charge/orbital order of the system. We identify a structural phase transition above the onset of charge/orbital order, frequently occurring extended defects and the temperature dependence and spatial distribution of charge/orbital ordering in the film. Our results show in detail the relationships between strain/defects and properties of the ordered phases and thus give important insights into how to tailor the functional properties of thin film junctions of strongly correlated materials.