Effect of dimension on charge order domain in Ruddlesden–Popper manganites

The charge order (CO) domains of dimensionally controlled manganites Pr1−xCaxMnO3 and Pr1−xCa1+xMnO4 (x=0.5, 0.6 and 0.67), which have three-dimensional (3D) and two-dimensional (2D) Mn–O networks, respectively, have been studied by transmission electron microscopy (TEM). Although the electron diffraction data show similar dependences of the modulation wave vector on hole doping x, there are distinctive differences between the 3D and 2D systems in terms of the CO domain sizes. In the 2D system, the TEM images show that the domain size is almost constant irrespective of hole doping x. On the other hand, in the 3D system, the domain size of the incommensurate CO for x=0.6 is much smaller than those of the commensurate CO for x=0.5 and 0.67. Namely, in the 3D system, the CO states are strongly influenced by the incommensurability for the parent lattice. This difference indicates that the dimension of the Mn–O network plays a crucial role in the CO domain and suggests that the electron–lattice coupling of the 3D system is stronger than that of the 2D system.