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    Atomic scale studies of La/Sr ordering in La2-2xSr1+2xMn2O7 single crystals

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    Type
    Conference Paper
    Authors
    Roldan, Manuel
    Oxley, Mark
    Li, Qiang
    Gray, Kenneth
    Mitchell, John
    Pennycook, Stephen
    Varela, Maria
    KAUST Department
    Imaging and Characterization Core Lab
    Date
    2016-12-20
    Permanent link to this record
    http://hdl.handle.net/10754/624997
    
    Metadata
    Show full item record
    Abstract
    Many fascinating properties of materials depend strongly on the local chemical environment. This is the case for many complex oxides, such as materials with colossal magnetoresistance, where small variations of composition at the atomic scale can affect drastically the macroscopic properties. The main objective of the present work is to analyze the local chemical composition with atomic resolution and to find out if any underlying chemical order is in any way connected to the magnetic properties of double perovskite La2-2xSr1+2xMn2O7 (LSMO) manganite oxides. For these compounds, charge and orbital ordering are observed for some doping values near x = 0.50 [1, 2]. For this purpose, we have use aberration corrected scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS) measurements and also theoretical simulations. We have compared different compositions within three distinct magnetic regions of the phase diagram: a ferromagnetic metallic sample with x=0.36, an insulating, antiferromagnetic (AF) x=0.56 and an additional AF x=0.50 sample which also exhibits charge ordering. High angle annular dark-field (HAADF) images, also known as Z-contrast, confirm that our single crystals exhibit high crystal quality. No secondary phases or defects are observed. Figure 1 displays an atomic resolution image obtained with the c-axis perpendicular to the electron beam of a x=0.50 sample. The perovskite (P)-like planes and the rock salt (R)-like planes are clearly observed, highlighted in green and red, respectively, on the image. The P-like planes exhibit a slightly high contrast, suggesting a possible La enrichment. EELS atomic resolution maps (inset) support a high degree of La segregation on those planes, while R-like planes are Sr rich. However, due to dechanneling of the beam, detailed image simulations are essential to accurately quantify the local chemical composition in an atomic column-by-atomic column fashion. For all our samples, we find a significant degree of long-range chemical ordering, which increases in the AF range. However, ordering is not complete and it cannot explain by itself the macroscopic electronic ordering phenomena [3].
    Citation
    Roldan M, Oxley M, Li Q, Gray K, Mitchell J, et al. (2016) Atomic scale studies of La/Sr ordering in La2-2xSr1+2xMn2O7 single crystals. European Microscopy Congress 2016: Proceedings: 1076–1077. Available: http://dx.doi.org/10.1002/9783527808465.emc2016.6566.
    Sponsors
    Research at Oak Ridge National Laboratory and at Argonne National Laboratory was sponsored by the US Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division. Research at Univ. Complutense was supported by the European Research Council. This work was supported in part by DOE grant No. DE-FG02-09R46554. The authors are thankful to M. Watanabe for the PCA plug in for Digital Micrograph
    Publisher
    Wiley
    Journal
    European Microscopy Congress 2016: Proceedings
    DOI
    10.1002/9783527808465.emc2016.6566
    Additional Links
    http://onlinelibrary.wiley.com/doi/10.1002/9783527808465.EMC2016.6566/abstract
    ae974a485f413a2113503eed53cd6c53
    10.1002/9783527808465.emc2016.6566
    Scopus Count
    Collections
    Conference Papers; Imaging and Characterization Core Lab

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