Berlin 2015 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 33: Low-Dimensional Systems: Other Materials
TT 33.6: Vortrag
Dienstag, 17. März 2015, 11:00–11:15, H 3010
Structural effects on charge order in single-layered manganites R1−xA1+xMnO4 — •Johannes Engelmayer, Holger Ulbrich, Lisa Weber, Markus Braden, and Thomas Lorenz — II. Physikalisches Institut, Universität zu Köln, Germany
Single-layered manganites show a complex interplay between charge, orbital, and magnetic degrees of freedom. For half-doped (x=1/2) R1−xA1+xMnO4 (R=Pr,La; A=Ca,Sr) the so-called Goodenough model is well established. This model proposes a site-centered charge order with a checkerboard pattern of Mn3+ and Mn4+ ions accompanied by an orbital order. Furthermore a magnetic order develops with ferromagnetic three-spin zig-zag chains and antiferromagnetic interchain coupling. For x=2/3 the charge order appears as stripe pattern with two adjacent stripes of Mn4+ ions alternating with a single stripe of Mn3+ ions, while in the magnetically ordered state four-spin zig-zag chains arise [1]. For a deeper understanding of the emergence of charge order, it is appropriate to vary on the one hand the elements R and A while keeping the doping level x constant—involving structural changes at fixed charge carrier density—and on the other hand change the doping level with the same R and A. Therefore various single crystals of R1−xA1+xMnO4 with R=(Pr, Nd, Sm, Tb), A=(Ca, Sr) and 0.5≤ x≤ 0.7 were grown and their structural parameters were determined by x-ray diffraction. Based on measurements of resistivity, magnetization, specific heat, and crystal structure we discuss the influence of structural variations on the ordering temperature.
[1] H. Ulbrich, M. Braden, Physica C 481, 31 (2012)