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

Handle URI:
http://hdl.handle.net/10754/624997
Title:
Atomic scale studies of La/Sr ordering in La2-2xSr1+2xMn2O7 single crystals
Authors:
Roldan, Manuel; Oxley, Mark; Li, Qiang; Gray, Kenneth; Mitchell, John; Pennycook, Stephen; Varela, Maria
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].
KAUST Department:
Imaging and Characterization Core Lab
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.
Publisher:
Wiley-Blackwell
Journal:
European Microscopy Congress 2016: Proceedings
Issue Date:
21-Dec-2016
DOI:
10.1002/9783527808465.emc2016.6566
Type:
Conference Paper
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
Additional Links:
http://onlinelibrary.wiley.com/doi/10.1002/9783527808465.EMC2016.6566/abstract
Appears in Collections:
Conference Papers; Advanced Nanofabrication, Imaging and Characterization Core Lab

Full metadata record

DC FieldValue Language
dc.contributor.authorRoldan, Manuelen
dc.contributor.authorOxley, Marken
dc.contributor.authorLi, Qiangen
dc.contributor.authorGray, Kennethen
dc.contributor.authorMitchell, Johnen
dc.contributor.authorPennycook, Stephenen
dc.contributor.authorVarela, Mariaen
dc.date.accessioned2017-06-14T12:17:32Z-
dc.date.available2017-06-14T12:17:32Z-
dc.date.issued2016-12-21en
dc.identifier.citationRoldan 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.en
dc.identifier.doi10.1002/9783527808465.emc2016.6566en
dc.identifier.urihttp://hdl.handle.net/10754/624997-
dc.description.abstractMany 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].en
dc.description.sponsorshipResearch 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 Micrographen
dc.publisherWiley-Blackwellen
dc.relation.urlhttp://onlinelibrary.wiley.com/doi/10.1002/9783527808465.EMC2016.6566/abstracten
dc.subjectcolossal magnetoresistanceen
dc.subjectscanning transmission electron microscopyen
dc.subjectcomplex oxidesen
dc.subjectelectron energy-loss spectroscopyen
dc.titleAtomic scale studies of La/Sr ordering in La2-2xSr1+2xMn2O7 single crystalsen
dc.typeConference Paperen
dc.contributor.departmentImaging and Characterization Core Laben
dc.identifier.journalEuropean Microscopy Congress 2016: Proceedingsen
dc.contributor.institutionApplied Physics III; Universidad Complutense de Madrid; Madrid Espagneen
dc.contributor.institutionMaterial Science & Technology Division; Oak Ridge National Laboratory; Oak Ridge Etats-Unisen
dc.contributor.institutionMaterial Science Division; Argonne National Laboratory; Chicago Etats-Unisen
dc.contributor.institutionMaterial Science & Engineering; National University of Singapore; Singapore Singapouren
kaust.authorRoldan, Manuelen
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