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

A.M.L. Lopes1,2, J.P. Araújo1,3, J.J. Ramasco4, E. Rita1,5, V.S. Amaral1,2, J.G. Correia1, R. Suryanarayanan6 and ISOLDE Collaboration1
1CERN EP, CH 1211 Geneve 23, Switzerland.
2Departamento de Física and CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
3Departamento de Física and IFIMUP, Universidade do Porto, 4169-007 Porto, Portugal.
4Physics Department, Emory University, Atlanta GA 30322, USA.
5ITN, E.N. 10, 2686-953 Sacavém, Portugal.
6Laboratoire de Physico-Chimie et de l'Etat Solide, Université Paris-Sud, 91405 Orsay, France.

(November 2005)

In this work, we report an atomic scale study on the ferromagnetic insulator manganite LaMnO3.12 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 (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 approx. 800 K and a low temperature regime where correlated regions have a weaker JT-distorted symmetry.