Dramatic effects of excess oxygen on physical properties and crystal structure of La0.95Sr0.05MnOy single crystal

We have examined the effects of excess oxygen on the magnetization, electrical transport properties and crystal structure of La0.95Sr0.05MnOy. An antiferromagnetic insulator phase confirmed in the as-grown crystal at low temperatures changed to a ferromagnetic insulator phase after the introduction of excess oxygen. The ferromagnetic transition temperature, TC, systematically increased with increasing oxygen content, y, due to an increase in the mean valence of manganese. However, the TC of crystals with excess oxygen was lower than that of the La1−xSrxMnO3.00 having identical manganese valence. This is considered to be a result of the competition among the mean valence of manganese, the concentration of cation vacancies, and the mean ionic radius of cations at the A-site.