Crystal Structure and Physical Properties of Oxygen Composition Controlled La$_{1-x}$Sr$_{x}$MnO$_{3+\delta }$ Single Crystals.

The La$_{1-x}$Sr$_{x}$MnO$_{3+\delta }$ is known to have various magnetic and crystal structures as functions of $x$. Although this system has relatively large oxygen nonstoichiometry, the effects of excess oxygen on the crystal structure and physical properties have not been well understood. In the present study, the crystal structure and physical properties of excess oxygen controlled La$_{1-x}$Sr$_{x}$MnO$_{3+\delta }$ single crystals were systematically studied. Single crystals with nominal compositions of La$_{1-x}$Sr$_{x}$MnO$_{3+\delta }$ (0.05 $\le \quad x \quad \le $ 0.2) were grown by the floating zone method. Thin plate-like crystals were obtained from the grown boules and controlled the oxygen content by post-annealing in various atmospheres. With increasing \textit{$\delta $}, the orthorhombic of the as-grown La$_{0.95}$Sr$_{0.05}$MnO$_{3+\delta }$crystal changed to the rhombohedral through pseudo-cubic orthorhombic. In addition, ferromagnetic behaviors appeared accompanying the CMR effect and $T_{C}$ increased as a function of \textit{$\delta $}. These are attributable to an increase of valence of Mn by excess oxygen. Relationships among the Sr substitution level, excess oxygen content, crystal structure and magnetic behaviors of La$_{1-x}$Sr$_{x}$MnO$_{3+\delta }$ will be discussed.