Charge and orbital ordered phases of La2-2xSr1+2xMn2O7-δ

Our studies have significantly modified the conventionally held view of the phase diagram of La2-2xSr1+2xMn2O7-delta for two compositions exhibiting charge (and orbital) order (CO), i.e., at hole-doping levels, h=x-delta, of similar to 0.5 and similar to 0.6. These CO states are stable over very narrow doping ranges (Delta h similar to +/- 0.005) at the lowest temperatures, but those ranges increase at higher temperatures (to Delta h similar to +/- 0.02) in a manner consistent with simple entropy considerations. Such narrow ranges dictate the crucial need for crystal homogeneity. Attesting to such homogeneity is a conductivity ratio of >10(10) upon crossing the first-order phase boundary from CO at h=0.60 to A-type antiferromagnetic (AAFM) at h similar to 0.59 or h similar to 0.61 plus two findings that were missed in the existing literature: that these CO phases are the ground state at the lowest temperatures, and for h similar to 0.5, that coexistence of the CO and AAFM phase is absent at any temperature.