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TT: Tiefe Temperaturen
TT 12: Correlated Electrons - Spin Systems and Itinerant Magnets: Experiment
TT 12.3: Talk
Saturday, March 5, 2005, 11:15–11:30, TU H2053
Magnetic Excitations in Layered Manganites — •D. Senff1, M. Benomar1, F. Krüger2, S. Scheidl2, Y. Sidis3, P. Reutler4,5, A. Revcolevschi5 und M. Braden1 — 1II. Physikalisches Institut, Universität zu Köln, Germany — 2Institut für Theoretische Physik, Universität zu Köln, Germany — 3Laboratoire Léon Brillouin, France — 4IfW Dresden, Germany — 5Laboratoire de Physico-Chimie de l’Etat Solide, Université
The most prominent member of the series La1−xSr1+xMnO4 is the half-doped compound with x=0.5. This system exhibits a very stable charge/orbital ordering, which at lower temperatures is accompanied by an antiferromagnetic ordering of ferromagnetic zig-zag chains, usually called CE-type order. We present the results of our experimental and theoretical work on the spin-wave spectrum in this phase.
Using inelastic neutron scattering we mapped out a large part of the magnetic excitation spectrum, which consists of one acoustic and two optic bands. All parts of the observed spectrum can be well described within linear spin-wave, taking account only two nearest-neighbor exchange constants, one ferromagnetic coupling J|| and an antiferromagnetic interaction J⊥. Our experimental data proof, that the intrachain coupling J|| is the dominant magnetic interaction in this system and we thus conclude that the CE-type ordering is driven by the underlying orbital ordering.
In addition, we want to discuss the spin-wave spectrum of the parent system LaSrMnO4 (x=0), which exhibits conventional G-type AFM-ordering, and compare the different coupling constants in these two compounds.