Phase Separation in A-site Ordered Perovskite Manganite LaBaMn$_2$O$_6$   Probed by $^{139}$La and $^{55}$Mn NMR
  $^{139}$La- and $^{55}$Mn-NMR spectra demonstrate that the ground state of the A-site ordered perovskite manganite LaBaMn$_2$O$_6$ is a spatial mixture of the ferromagnetic (FM) and antiferromagnetic (AFI(CE)) regions, which are assigned to the metallic and the insulating charge ordered state, respectively. This exotic coexisting state appears below 200 K via a first-order-like formation of the AFI(CE) state inside the FM one. Mn spin-spin relaxation rate indicates that the FM region coexisting with the AFI(CE) one in LaBaMn$_2$O$_6$ is identical to the bulk FM phase of the disordered form La$_{0.5}$Ba$_{0.5}$MnO$_3$ in spite of the absence of A-site disorder. This suggests mesoscopic rather than nanoscopic nature of FM region in LaBaMn$_2$O$_6$\@. 
Y. Kawasaki, T. Minami, Y. Kishimoto, T. Ohno, K. Zenmyo, H. Kubo, T.   Nakajima and Y. Ueda