Interface and Surface Cation Stoichiometry Modified by Oxygen Vacancies in Epitaxial Manganite Films

Perovskite manganites are viewed as one of the key building blocks of oxide spintronics devices due to their attractive physical properties. However, cation off-stoichiometry at epitaxial interfaces between manganites and other materials can lead to interfacial dead layers, severely reducing the device performance. Here, transmission electron microscopy and synchrotron-based spectroscopy are used to demonstrate that oxygen vacancies during growth serve as a critical factor for modifying the cation stoichiometry in pulsed laser deposited La 0.8Sr 0.2MnO 3 films. Near the film/substrate (SrTiO 3) interface, A-site cations (La/Sr) are in excess when oxygen vacancies are induced during film growth, partially substituting Mn. Simultaneously, Sr cations migrate towards the film surface and form a SrO rock-salt monolayer. Consequentially, a gradient of the Mn nominal valence is observed along the film growth direction, leading to anomalous magnetic properties. The results narrow the selection range of useful oxygen pressures during deposition and demonstrate that accurate cation stoichiometry can only be achieved after oxygen vacancies are eliminated during growth. This finding suggests that the oxygen pressure serves as a tuning parameter for the interfacial dead layers and, hence, for control over device properties. During film growth, oxygen vacancies modify the cation stoichiometry in pulsed laser deposited La 0.8Sr 0.2MnO 3 films. Mn is partially substituted by La/Sr cations near strained interfaces, leading to a gradient in the Mn nominal valence along the film growth direction. Without elimination of oxygen vacancies during growth, anomalous magnetic properties will prevent the controlled fabrication of spintronic devices