Common features of nanoscale structural correlations in magnetoresistive manganites with ferromagnetic low-temperature state

We report x-ray scattering studies of nanoscale structural correlations in Nd$_{1-x}$Sr$_x$MnO$_3$ and La$_{1-x}$(Ca,Sr)$_x$MnO$_3$, $x$=0.2--0.5. We find that the correlated regions possess a temperature-independent correlation length of 2-3 lattice constants which is the same in all samples. The period of the lattice modulation of the correlated regions is proportional to the Ca/Sr doping concentration $x$. Remarkably, the lattice modulation periods of these and several other manganites with a ferromagnetic ground state fall on the same curve when plotted as a function of $x$. Thus, the structure of the correlated regions in these materials appears to be determined by a single parameter, $x$. We argue that these observations provide important clues for understanding the Colossal Magnetoresistance phenomenon in manganites.