“Cation Stoichiometry, Microstructure and Properties Tuned by Oxygen Vacancies in Epitaxial Manganite and Manganite-based Heterostructures”

La_1-xSr_xMnO₃ is viewed as one of the key building blocks of oxide spintronics devices due to its rich physical properties. However, when manganite and other materials are engineered together, the induced interfacial dead layer can reduce the device performance such as the tunneling current or magnetoelectric coupling effect. In this study, transmission electron microscopy and spectroscopic techniques were used to demonstrate that the oxygen vacancies during film growth can serve as a critical factor in tuning the cation stoichiometry in pulsed laser deposited La_0.8Sr_0.2MnO₃ films. When the oxygen vacancies are induced, A-site cations (La/Sr) are in excess near film/substrate interface. Simultaneously, SrO rocksalt monolayer is formed due to the migration of the Sr cations. Consequently, a gradient of Mn nominal valence is observed along the film growth direction according to the electron energy loss spectroscopy results. This finding suggests that the oxygen pressure serves as one extrinsic tuning parameter for the interfacial dead layer and hence control over device properties.