Effect of dimension on charge order domain in RuddlesdenPopper manganites

The charge order (CO) domains of dimensionally controlled manganites Pr_1-xCa_xMnO₃ and Pr_1-xCa _1xMnO₄ (x=0.5, 0.6 and 0.67), which have three-dimensional (3D) and two-dimensional (2D) MnO 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 MnO network plays a crucial role in the CO domain and suggests that the electronlattice coupling of the 3D system is stronger than that of the 2D system.