Orbital and charge ordering in La1-xSr1+xMnO4 (0.4 <= x <= 0.5)

Hole concentration dependence of charge order (CO) and orbital order (OO) i n layered perovskite compounds La1-xSr1+xMnO4 has been studied by means of the resonant X-ray scattering technique. Both CO and OO are observed below 210 K in the compounds having the hole concentration x between 0.5 and 0.48 , but neither is observed for x less than or equal to 0.46. The transition temperatures are nearly independent of x between 0.5 and 0.48. Correlation lengths xi 's for both orders obtained from analyses of superlattice peak p rofiles are finite at any temperature, Moreover, in contrast to the cubic p erovskite, xi for OO is larger than that for CO. xi for OO is as short as t hat for CO at the critical concentration of x = 0.48. These results suggest that OO is prerequisite to the forming of CO in this system.