Percolative transition on ferromagnetic insulator manganites: Uncorrelated to correlated polaron clusters

We report an atomic-scale study on the ferromagnetic insulator manganite LaMnO3.12 using γ-γ perturbed angular correlation spectroscopy. Data analysis reveals a nanoscopic transition from an undistorted to a Jahn-Teller (JT) distorted local environment upon cooling. The percolation thresholds of the two local environments enclose a macroscopic structural transition (rhombohedral-orthorhombic). Two distinct regimes of JT distortions were found: a high-temperature regime where uncorrelated polaron clusters with severe distortions of the Mn³⁺O₆ octahedra survive up to T≈8000.3em0exK and a low-temperature regime where correlated regions have a weaker JT-distorted symmetry.