STUDY OF THE LAYERED MAGNETORESISTIVE PEROVSKITE LA1.2SR1.8MN2O7 BY HIGH-RESOLUTION ELECTRON-MICROSCOPY AND SYNCHROTRON X-RAY-POWDER DIFFRACTION

The layered manganite La1.2Sr1.8Mn2O7 is important in that it displays giant negative magnetoresistance properties, and its study complement s the growing body of what we know about the complex size-charge-tempe rature-magnetic field parameter space of the perovskites A(1-x)(III)A' (xMnO3)-Mn-II. We report here the results of a detailed. characterizat ion of the microstructure and structure of this layered phase by high- resolution electron microscopy and synchratron X-ray powder diffractio n (SXPD). The high resolution of the data has permitted the quantifica tion of stacking faults. The SXPD data have also been treated using Ri etveld analysis. We reexamine the magnetic and transport properties of this phase. The study highlights the importance of the two-dimensiona l (2D) nature of the title phase.