Regensburg 2004 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 24: Postersitzung III: Korrelierte Elektronen, ”Orbital Physics”
TT 24.50: Poster
Mittwoch, 10. März 2004, 14:30–19:00, Poster A
Orbital-spin coupling in La1−xSr1+xMnO4 observed by Raman spectroscopy — •K.-Y. Choi1, D. Heydhausen1, T. Sahaoui1, P. Reutler2, B. Büchner2, P. Lemmens1,3, and G. Güntherodt1 — 12. Physikalisches Institut, RWTH Aachen — 2Institute for Solid State Research, IFW Dresden — 3MPI for Solid State Research, Stuttgart
We present an inelastic light scattering study of the layered manganites La1−xSr1+xMnO4 (x=0 and 1/8). The samples have the K2NiF4-type tetragonal structure (symmetry group I4/mmm ) and show a C-type antiferromagnetic ordering at TN≈ 125 K for x=0 as well as of an orbital ordering with a dominant character of the d3z2−r2 orbital. The undoped sample shows a pronounced two-magnon spectrum (2MS) in the ab plane. The 2MS undergoes a strong damping already above 1.5 TN and evolves into quasielastic scattering consisting of two components. The latter implies the rapid suppression of short-range antiferromagnetic correlations while there appear other magnetic correlations. In addition, a symmetry-forbidden phonon mode is observed around 700 cm−1 in the high-temperature region for in-plane polarizations. Surprisingly, new modes appear upon cooling below TN. This is due to zone-folded modes induced by the formation of a superstructure. This provides evidence for induced orbital ordering through spin-orbital coupling in the plane. As to x=1/8 the 2MS is totally suppressed while activated phonon modes develop which are not Raman-active for x=0. This feature is discussed in terms of the mixture of dx2−y2 with d3z2−r2 orbitals as well as of the motion of holes. Work supported by DFG SPP1073