# Topotactic Phase Transition in Epitaxial La0.7Sr0.3MnO3‐δ Films Induced by Oxygen Getter Assisted Thermal Annealing

## TL;DR

A new method using aluminum to remove oxygen from La0.7Sr0.3MnO3-δ films triggers a structural and magnetic phase transition.

## Contribution

A simple thermal vacuum annealing method using aluminum as an oxygen getter is introduced for inducing topotactic phase transitions.

## Key findings

- X-ray Diffraction confirms a PV to BM phase transition in La0.7Sr0.3MnO3-δ thin films.
- The material transitions from ferromagnetic to antiferromagnetic and metallic to insulating states.
- Surface segregation and cation redistribution are observed via advanced microscopy techniques.

## Abstract

Oxygen vacancies play a crucial role in controlling the physical properties of complex oxides. In La0.7Sr0.3MnO3‐δ, the topotactic phase transition from Perovskite (PV) to Brownmillerite (BM) can be triggered, e.g., via oxygen removal during thermal annealing. Here, a very efficient thermal vacuum annealing method is reported 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‐δ thin films grown via physical vapor deposition. The efficiency of this method is confirmed using La0.7Sr0.3MnO3‐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 are 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.

The perovskite to brownmillerite topotactic phase transition in La0.7Sr0.3MnO3‐δ thin films is achieved through a simple and efficient thermal vacuum annealing that employs bulk aluminum as an active oxygen getter. STEM reveals surface segregation and cation redistribution, while EELS identifies distinct manganese oxidation states across different regions.