Orbital correlations in doped manganites
Hill JP, Nelson CS, von Zimmermann M, Kim YJ, Gibbs D, Casa D, Keimer B, Murakami Y, Venkataraman C, Gog T, Tomioka Y, Tokura Y, Kiryukhin V, Koo TY, Cheong SW
APPLIED PHYSICS AMATERIALS SCIENCE & PROCESSING 
73 (6): 723730 DEC 2001 


Abstract:
We review our recent Xray scattering studies of charge and orbital order in doped manganites, with specific emphasis on the role of orbital correlations in Pr1_xCaxMnO3. For x = 0.25, we find an orbital structure indistinguishable from the undoped structure and longrange orbital order at low temperatures. For dopings 0.3 less than or equal to x less than or equal to 0.5, we find scattering consistent with a charge and orbitally ordered CEtype structure. While in each case the charge order peaks are resolution limited, the orbital order exhibits only shortrange correlations. We report the doping dependence of the correlation length and discuss the connection between the orbital correlations and the finite magnetic correlation length observed on the Mn3+ sublattice with neutronscattering techniques. The physical origin of these domains, which appear to be isotropic, remains unclear. We find that weak orbital correlations persist well above the phase transition, with a correlation length of 12 lattice constants at high temperatures. Significantly, we observe similar correlations at high temperatures in La0.7Ca0.3MnO3, which does not have an orbitally ordered ground state, and we conclude that such correlations are robust to variations in the relative strength of the electronphonon coupling.