Dresden 2006 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 25: Correlated Electrons - Poster Session
TT 25.114: Poster
Mittwoch, 29. März 2006, 14:30–18:30, P1
Charge, spin and orbital degrees of freedom in La2−xSrxCoO4 — •M. Cwik1, M. Haider1, M. Benomar1, M. Reuther1, A. Hoser2, Y. Sidis3, T. Lorenz1, and M. Braden1 — 1II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln — 2Institut für Festkörperforschung, Forschungszentrum Jülich, D-52425 Jülich — 3Laboratoire Leon Brillouin (CEA-CNRS), CEA-Saclay, 91191 Gif-Sur-Yvette Cedex, France
The layered cobaltate La2CoO4 is an orthorhombic distorted antiferromagnetic insulator with TN∼ 270 K and Co2+ (3d7) in the S=3/2 high spin state [1]. The substitution of La3+ by larger Sr2+ ions reduces the orthorhombic distortion, suppresses long range magnetic order and induces a nominal Co2+/Co3+ mixed valency. For La1.5Sr0.5CoO4 a checkerboard-like charge order (Tc ∼ 750 K) and an antiferromagnetic order (Ts ∼ 30 K) with the propagation vector Q=(0.25 0.25 1) have been found [2]. We present an analysis of the crystal structure, of the spin and charge order and of the magnetic correlations studied on single crystals for 0.1 ≤ x ≤ 1.0. For x = 0.4 the magnetic order is incommensurate but we do not find evidence for a stripe-like ordering scheme similar to the observations in cuprates or nickelates. We interpret the different magnetic ordering , the emerging charge order and the structural anomalies in this system in terms of the Co3+ spin degree of freedom, several magnetic interaction parameters and geometrical frustration.
[1] K. Yamada et al., Phys. Rev. B 39, 2236 (1989)
[2] I. A. Zaliznyak et al., Phys. Rev. Lett. 85, 4353 (2000) This work is supported by the DFG through SFB 608.