STEM Studies of Charge and Orbital Ordering in La_0.6Sr_2.4Mn₂O₇ Manganite

Charge and orbital ordering typically occurs in perovskite-related oxides, and has been demonstrated to induce various interesting physical phenomena. La_2−2xSr_1+2xMn₂O₇ represents one of the most interesting manganites where its charge and orbital ordering can be tuned by varying x. Specifically, no long-range magnetic order of any type was found using neutron powder diffraction for 0.66 ≤ x ≤ 0.72 in polycrystalline samples. In this study, we perform systematic scanning transmission electron microscopy (STEM) studies of charge and orbital ordering and local nano-scale phase competition in a La_0.6Sr_2.4Mn₂O₇ (x = 0.7) single crystal. By combining lattice strain quantification and valence state mapping at atomic scale for this crystal, we show that charge and orbital ordering at short-ranges can be probed using real-space imaging and spectroscopy. Charge ordering stripes of Mn³⁺ and Mn⁴⁺ are directly visualized by electron-energy loss spectroscopy and found to be spatially correlated with periodic picometer-level shear deformations via orbital ordering in Mn³⁺ stripes.