Tailoring c-axis orientation in epitaxial Ruddlesden-Popper Pr0.5Ca1.5MnO4 films

Abstract

Abstract Interest in layered Ruddlesden–Popper (RP) strongly correlated manganites of Pr0.5Ca1.5MnO4 as well as in their thin film polymorphs is motivated by the high temperature of charge orbital ordering above room temperature. The c‐axis orientation in epitaxial films is tailored by different SrTiO3 (STO) substrate orientations and CaMnO3 (CMO) buffer layers. Films on STO(110) show in‐plane alignment of the c‐axis parallel to the [100] direction. On STO(100), two possible directions of the in‐plane c‐axis lead to a mosaic like, quasi 2D nanostructure, consisting of RP, rock‐salt, and perovskite blocks. With the CMO buffer layer, Pr0.5Ca1.5MnO4 epitaxial films with c‐axis out‐of‐plane are realized. Different physical vapor deposition techniques as ion beam sputtering, pulsed laser deposition and metalorganic aerosol deposition are applied in order to distinguish effects of growth conditions from intrinsic epitaxial properties. Despite their very different growth conditions, surface morphology, crystal structure, and orientation of the thin films reveal a high level of similarity as verified by X‐ray diffraction, scanning, and high resolution transmission electron microscopy. For different epitaxial relations stress in the films is relaxed by means of modified interface chemistry. The charge ordering in the films occurs at a temperature close to that expected in bulk material.

The growth direction of a Ruddlesden–Popper Pr0.5Ca1.5MnO4 thin film is governed by its strain state. For different SrTiO3 substrate orientations the unit cells of the film are aligned in parallel or in a perpendicular configuration—forming a mosaic like microstructure. With a CaMnO3 buffer layer the c‐axis can even be tilted to the out‐of‐plane direction. image