Features of highly correlated electronic states in the simple perovskite manganite Sr_1-xSm_xMnO₃ with 0.15 ≤ x ≤ 0.50

The C- and A-type antiferromagnetic orderings have been reported in the highly correlated electronic manganite Sr1-xSmxMnO₃ (SSMO) with the simple perovskite structure in the composition range of 0.34 ≤ x ≤ 0.46. Because these antiferromagnetic orderings should be coupled to orbital orderings, the crystallographic features of SSMO samples prepared with 0.15 ≤ × ≤ 0.50 have been investigated, mainly by X-ray powder diffraction and transmission electron microscopy, to understand the detailed features of the corresponding orbital-ordered states. It was found that around 100 K, for instance, the C-type orbital-ordered (COO) state was observed for 0.15 ≤ x ≤ 0.42, the orbital-modulated (OM) state for 0.44 ≤ x < 0.50, and the coexistence state of both ferromagnetic Pnma (I) and paramagnetic Pnma (II) regions for x = 0.50, where the OM state was characterized by a transverse lattice modulation with an incommensurate periodicity. Neither the A-type orbital-ordered state nor the CE-type state involving both orbital and charge modulations was found in the SSMO samples. The reasons for their absence are also discussed on the basis on the experimental data obtained in this study.