Topotactic phase transition in epitaxial La_0.7Sr_0.3MnO_3-δ films induced by oxygen getter assisted thermal annealing

Oxygen vacancies play a crucial role in controlling the physical properties of complex oxides. In La_0.7Sr_0.3MnO_3-δ, the topotactic phase transition from Perovskite (PV) to Brownmillerite (BM) can be triggered e.g. via oxygen removal during thermal annealing. Here we report on a very efficient thermal vacuum annealing method using aluminum as an oxygen getter material. The topotactic phase transition is characterized by X-ray Diffraction which confirms a successful transition from PV to BM in La_0.7Sr_0.3MnO_3-δ thin films grown via physical vapor deposition. The efficiency of this method is confirmed using La_0.7Sr_0.3MnO_3-δ micron-sized bulk powder. The accompanying transition from the original Ferromagnetic (FM) to an Antiferromagnetic (AF) state and the simultaneous transition from a metallic to an insulating state is characterized using Superconducting Quantum Interference Device (SQUID)-magnetometry and Alternating Current (AC) resistivity measurements, respectively. The near surface manganese oxidation states are probed by synchrotron X-ray Absorption Spectroscopy. Moreover, X-ray Reflectivity, Atomic Force Microscopy and Scanning Transmission Electron Microscopy reveal surface segregation and cation redistribution during the oxygen getter assisted annealing process.