Evidence for nano-scale inhomogeneities in bilayer manganites in the Mn4+ rich region: 0.54≤x≤0.80 Original Research Article

The atomic pair distribution function (PDF) technique is employed to probe the atomic local structural responses in naturally double layered manganites La2−2xSr1+2xMn2O7 in the doping range 0.54≤x≤0.80. Our low temperature neutron powder diffraction measurements suggest the coexistence of two different Jahn-Teller (JT) distorted MnO6 octahedra when its ordered magnetic structure crosses over from type A (0.54≤x≤0.66) to type C/C* (0.74≤x≤0.90) ordering. At all doping levels at low temperature the doped holes reside predominantly in the plane of the bilayer. In the type A magnetic ordering regime, the eg electrons appear to be significantly delocalized in the plane resulting in undistorted octahedra, while in type C/C* regime, elongated JT distorted octahedra are apparent. This is consistent with the presence of inhomogeneous coexisting delocalized and localized electronic states. No evidence of macroscopic phase separation has been observed. Such nanoscale inhomogeneities may explain the magnetically frustrated behavior observed in the spin disordered ‘gap’ region (0.66≤x≤0.74).