Measurements of magnetization, electrical resistivity, and synchrotron x-ray diffraction were performed on single crystals of ${\mathrm{Bi}}_{1-x}{\mathrm{Sr}}_x\mathrm{Mn}{\mathrm{O}}_3$ $(0.35⩽x⩽0.64)$. The resistivity and magnetization curves show a kink near $570\mathrm{K}$ and an anomaly which is accompanied by a hysteresis at $400–500\mathrm{K}$ for all samples. Synchrotron x-ray diffraction of a sample with $x=0.47$ indicates that the kink and the anomaly are ascribed to an orbital- and a charge-ordering phase transition, respectively. Orbital ordering becomes incommensurate above the charge-ordering transition temperature, which is not reported in other perovskite manganese oxides. Magnetization measurements show an antiferromagnetic transition near $150\mathrm{K}$. Below $40\mathrm{K}$, a spin-glass-like behavior is observed for $0.35⩽x⩽0.53$. We also investigated the anisotropic properties of a single-domain crystal with $x=0.47$. Magnetic anisotropy below the Néel temperature implies that the Mn spin moments orient themselves along the $c$ axis. Anisotropic electrical conduction starts appearing below $570\mathrm{K}$, which is the orbital-ordering transition temperature. This anisotropy is enhanced below charge-ordering temperature and is approximately ${\rho }_{ab}∕{\rho }_c\simeq 10$ at room temperature, which indicates that $e_g$ electrons on excess ${\mathrm{Mn}}^{3+}$ ions move more easily along the $c$ axis than in the $ab$ plane.

• Received 13 March 2007

DOI:https://doi.org/10.1103/PhysRevB.75.214431