Topotactic phase transition in epitaxial La0.7Sr0.3MnO3-{\delta} films induced by oxygen getter assisted thermal annealing

TL;DR

This study demonstrates an efficient oxygen getter-assisted thermal annealing method to induce a topotactic phase transition from Perovskite to Brownmillerite in La0.7Sr0.3MnO3-{ extdelta} films, significantly altering their magnetic and electronic properties.

Contribution

The paper introduces a novel, highly effective annealing technique using aluminum as an oxygen getter to control phase transitions in complex oxide films.

Findings

Successful PV to BM phase transition confirmed by XRD

Transition from ferromagnetic to antiferromagnetic state observed

Metallic to insulating transition characterized by resistivity measurements

Abstract

Oxygen vacancies play a crucial role in controlling the physical properties of complex oxides. In La0.7Sr0.3MnO3-{\delta}, 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 La0.7Sr0.3MnO3-{\delta} thin films grown via physical vapor deposition. The efficiency of this method is confirmed using La0.7Sr0.3MnO3-{\delta} 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.