A checkerboard orbital-stripe phase and charge ordering transitions in Pr(SrxCa2-x)Mn2O7 (0 ≤ x ≤ 0.45)

The charge/orbital ordering (COO) behaviors in the double-layered Pr(SrxCa2-x)Mn2O7 have been investigated by in situ transmission electron microscopy (TEM) observations. The experimental results reveal that two charge ordering (CO) phase transitions, so-called T-co1 and T-co2, commonly exist in the orthorhombic Pr(SrxCa2-x)Mn2O7 (0 <= x <= 0.45) samples. Moreover, a checkerboard orbital-stripe phase characterized by two orthogonal COO modulations, q(a) and q(b), is observed between T-co1 and T-co2 in all samples. Detailed TEM investigations on the x=0.2 sample, in which a visible electric polarization was found (TOKUNAGA Y. et al., Nat. Mater., 5 (2006) 937) demonstrate that the q(b) modulation only survives between T-co1 and T-co2, and the checkerboard phase transforms into the conventional one-dimensional COO stripe phase below T-co2. The reversal of in-plane optical anisotropy across the T-co2 transition (TOKUNAGA Y. et al., Nat. Mater., 5 (2006) 937) is also explained based on TEM result. Copyright (C) EPLA, 2009