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

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 $T\approx 800K$ and a low temperature regime where correlated regions have a weaker JT-distorted symmetry.

4 pages, 4 Figures, submitted to PRL, new version with more data, text reformulated