Re-entrant charge-ordering behaviour in the layered manganites La2-2xSr1+2xMn2O7

We have investigated the charge-ordering (CO) behaviour of the layered mang anites La2-2xSr1+2xMn2O7 (0.3 less than or equal to x less than or equal to 0.8) by means of transport and magnetization measurements. It is found tha t the CO transitions occur in the vent high-temperature region (200-340 K) and moreover the re-entrant CO behaviours are exhibited over a broad doping range (0.47 less than or equal to x less than or equal to 0.62). The elect ronic phase diagram based on the transport data shows features similar to t hose suggested by a two-dimensional Hubbard model with electron-phonon inte raction (Yuan Q and Thalmeier P 1999 Phys. Rev. Lett. 83 3502). Our present results reveal that the temperature-dependent polaron bandwidth plays a cr ucial role as regards the occurrence of re-entrant CO transitions in the la yered manganites.