The Jahn-Teller effect of layered perovskite manganites La2-2xSr1+2xMn2O7 studied by mn K-edge XAFS

The lattice distortion and local symmetry of bilayered perovskite manganites play an important role in its magnetoelectric transport properties, in particular, the effect of the colossal magnetoresistance (CMR) found in this new member of CMR family. In order to explore the structural origin, X-ray absorption fine structure (XAFS) spectra at both near edge and extended part were measured at Mn K-edge of the bilayered perovskite manganites, La2-2xSr1 +2xMn2O7 with x = 0.2, 0.3, 0.33, 0.4, 0.5 and 0.6. The XAFS oscillations from the first coordination shell of Mn-O were filtered out and analyzed in more detail aimed at investigating the lattice distortion with respect to this Mn-O octahedron. Despite lattice shrinkage due to substitution of La with Sr which has to be a close atom radius, the largest derivation from the Gaussian distribution of the Mn-O shell arose from the 0.33 doped sample. In a more sophisticated fit, we found that the JT distortion magnitude Delta(JT) and Debye-Waller factors sigma(2)(1) and sigma(2)(2) are the highest at the same doping concentration x = 0.33. (c) 2005 Elsevier B.V. All rights reserved.