Percolative phase transition on ferromagnetic insulator manganites: uncorrelated to correlated polaron clusters

TL;DR

This study uses PAC spectroscopy to investigate local structural changes in ferromagnetic insulator manganite LaMnO$_{3.12}$, revealing a transition from uncorrelated to correlated polaron clusters associated with a macroscopic structural phase change.

Contribution

It provides the first atomic-scale evidence of a percolative phase transition involving polaron clusters in manganites, linking local distortions to macroscopic structural phases.

Findings

Identification of a nanoscopic transition from undistorted to Jahn-Teller-distorted environments.

Discovery of two regimes of Jahn-Teller distortions with different correlation levels.

Observation of polaron clusters surviving up to 800 K in the high-temperature regime.

Abstract

In this work, we report an atomic scale study on the ferromagnetic insulator manganite LaMnO$_{3.12}$ using $\gamma-\gamma$ PAC spectroscopy. Data analysis reveals a nanoscopic transition from an undistorted to a Jahn-Teller-distorted local environment upon cooling. The percolation thresholds of the two local environments enclose a macroscopic structural transition (Rhombohedric-Orthorhombic). Two distinct regimes of JT-distortions were found: a high temperature regime where uncorrelated polaron clusters with severe distortions of the Mn$^{3+}$O$_{6}$ octahedra survive up to $T \approx 800 K$ and a low temperature regime where correlated regions have a weaker JT-distorted symmetry.