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

A.M.L. Lopes^1,2, J.P. Araújo^1,3, J.J. Ramasco⁴, E. Rita^1,5, V.S. Amaral^1,2, 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 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 (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.

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