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Atomic Scale Studies of La/Sr Ordering in Colossal Magnetoresistant La2−2xSr1+2xMn2O7 Single Crystals

Published online by Cambridge University Press:  29 September 2014

Manuel A. Roldan ,
Mark P. Oxley ,
Qing’an Li ,
Hong Zheng ,
K. E. Gray ,
J. F. Mitchell ,
Stephen J. Pennycook  and
María Varela
Manuel A. Roldan*
Affiliation:
Dpto. Física Aplicada III, Universidad Complutense de Madrid, 28040 Madrid, Spain Oak Ridge National Laboratory, Materials Science and Technology Division, Oak Ridge, TN 37831, USA
Mark P. Oxley
Affiliation:
Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37212, USA
Qing’an Li
Affiliation:
Argonne National Laboratory, Materials Science Division, Argonne, IL 60439, USA
Hong Zheng
Affiliation:
Argonne National Laboratory, Materials Science Division, Argonne, IL 60439, USA
K. E. Gray
Affiliation:
Argonne National Laboratory, Materials Science Division, Argonne, IL 60439, USA
J. F. Mitchell
Affiliation:
Argonne National Laboratory, Materials Science Division, Argonne, IL 60439, USA
Stephen J. Pennycook
Affiliation:
Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996, USA
María Varela
Affiliation:
Dpto. Física Aplicada III, Universidad Complutense de Madrid, 28040 Madrid, Spain Oak Ridge National Laboratory, Materials Science and Technology Division, Oak Ridge, TN 37831, USA
*
*Corresponding author. marolgu@gmail.com
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Abstract

To date, it is unclear whether chemical order (or disorder) is in any way connected to double exchange, electronic phase separation, or charge ordering (CO) in manganites. In this work, we carry out an atomic resolution study of the colossal magnetoresistant manganite La2−2xSr1+2xMn2O7 (LSMO). We combine aberration-corrected electron microscopy and spectroscopy with spectroscopic image simulations, to analyze cation ordering at the atomic scale in real space in a number of LSMO single crystals. We compare three different compositions within the phase diagram: a ferromagnetic metallic material (x=0.36), an insulating, antiferromagnetic charge ordered (AF-CO) compound (x=0.5), which also exhibits orbital ordering, and an additional AF sample (x=0.56). Detailed image simulations are essential to accurately quantify the degree of chemical ordering of these samples. We find a significant degree of long-range chemical ordering in all cases, which increases in the AF-CO range. However, the degree of ordering is never complete nor can it explain the strongly correlated underlying ordering phenomena. Our results show that chemical ordering over distinct crystallographic sites is not needed for electronic ordering phenomena to appear in manganites, and cannot by itself explain the complex electronic behavior of LSMO.

Keywords

colossal magnetoresistancescanning transmission electron microscopycomplex oxideselectron energy-loss spectroscopy
Type
Materials Applications
Information
Microscopy and Microanalysis , Volume 20 , Issue 6 , December 2014 , pp. 1791 - 1797
Copyright
© Microscopy Society of America 2014 

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