Charge-ordering-induced polar domains and domain walls in a bilayered manganite Pr(Sr0.15Ca0.85)2Mn2O7

We have observed charge-ordering-induced polar domains and domain walls (DWs) in a bilayered manganite Pr(Sr0.15Ca0.85)(2)Mn2O7 using second-harmonic-generation microscopy. Around the transition temperature T-C similar to 306 K, a nucleation process of the domains with spontaneous polarization is clearly observed. Well below T-C, the characteristic band-shaped dark patterns are identified in the second-harmonic images. On the analogy of the nucleation feature, they can be assigned to the DWs separating antiparallel polar domains. The anisotropy in the DW is governed by the geometrical constraint of the charge and orbital ordering, not by the electrostatic stability as in conventional ferroelectric DWs.