We present high-resolution high-energy and resonant x-ray-diffraction results from ${\mathrm{La}}_{2-2x}{\mathrm{Sr}}_{1+2x}{\mathrm{Mn}}_2{\mathrm{O}}_7$ for $x=0.55$, 0.575, and 0.60. These compounds show superlattice reflections at wave vectors of $(h\pm \delta ,k\pm \delta ,l)$ and $(h\pm 2\delta ,k\pm 2\delta ,l)$, arising from orbital ordering with associated Jahn-Teller distortions and charge ordering, respectively. We observe a phase transition boundary between the $x=0.55$ and $x=0.575$ doping levels. Samples with $x=0.55$ display structural characteristics similar to those previously reported for $x=0.5$. Compared to this the long-range order in samples with $x=0.55$ and $x=0.6$ have a distinct change in wave-vector and correlation length. We attribute this to a new orbital bi-stripe phase, accompanied by weak, frustrated, charge ordering. The observed azimuthal dependence of the orbital order reflection supports the model proposed for this new phase.

• Received 2 December 2004

DOI:https://doi.org/10.1103/PhysRevB.72.064432