Orbital Bi-Stripes in High Doped Bilayer Manganites

TL;DR

This study investigates orbital bi-stripe phases in highly doped bilayer manganites using advanced x-ray diffraction, revealing a new orbital ordering phase with distinct wavevector changes and weak charge order at specific doping levels.

Contribution

It reports the discovery of a novel orbital bi-stripe phase in high doped bilayer manganites, characterized by unique wavevector and correlation changes, supported by azimuthal dependence analysis.

Findings

Identification of superlattice reflections indicating orbital and charge ordering.

Observation of a phase transition between x=0.55 and x=0.575 doping levels.

Detection of a new orbital bi-stripe phase with weak charge ordering.

Abstract

We present high resolution high energy and resonant x-ray diffraction results from La2-2xSr1+2xMn2O7 for x=0.55,0.575 and 0.60. These compounds show superlattice reflections at wavevectors of (h+-\delta,k+-\delta,l) and (h+-2\delta,k+-2\delta,l), arising from orbital ordering with associated Jahn-Teller distortions and charge ordering respectively. We observe a phase transition 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 wavevector and correlation. We attribute this to a new orbital bi-stripe phase, accompanied by weak, frustrated, charge ordering. The observed azimuthal dependence of the orbital order reflections supports the model proposed for this new phase.