Percolative phase transition on ferromagnetic insulator manganites:   uncorrelated to correlated polaron clusters
  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. 
A.M.L. Lopes, J.P. Araujo, J.J. Ramasco, E. Rita, V.S. Amaral, J.G.   Correia, R. Suryanarayanan and the ISOLDE Collaboration