Dresden 2009 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 6: Postersession Correlated Electrons: (General) Theory, Low-Dimensional Systems, Kondo Physics, Heavy Fermions, Quantum-Critical Phenomena

TT 6.19: Poster

Montag, 23. März 2009, 13:00–16:45, P1A

Low temperature magnetism of La_1−xSr_xCoO₃ (x∼ 0.002) — •V. Kataev¹, A. Alfonsov¹, E. Vavilova^1,2, B. Büchner¹, A. Podlesnyak³, M. Russina³, A. Furrer⁴, Th. Strässle⁴, E. Pomjakushina^4,5, K. Conder⁵, and D.I. Khomskii⁶ — ¹IFW Dresden, D-01171 Dresden, Germany — ²Zavoisky Physical Technical Institute, RAS, 420029 Kazan, Russia — ³Hahn–Meitner–Institut, D-14109 Berlin, Germany — ⁴Laboratory for Neutron Scattering, ETH Zürich & PSI, CH-5232 Villigen PSI, Switzerland — ⁵Laboratory for Developments and Methods, PSI, CH-5232 Villigen PSI, Switzerland — ⁶II. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany

We present results of electron spin- (ESR), nuclear magnetic resonance (NMR) and inelastic neutron scattering (INS) studies of single crystals of La_1−xSr_xCoO₃. In contrast to LaCoO₃, which is nonmagnetic at T 30 K, a very small Sr²⁺ doping (x∼ 0.002) yields a strong magnetization already at low T. ⁵⁹Co NMR measurements indicate the formation of extended magnetic clusters in this temperature regime. ESR spectroscopy reveals multiple gapped resonance excitations with different g-factor values suggesting that magnetic clusters have a large spin multiplicity and substantial spin-orbital coupling. The Q-dependence of the INS intensity gives evidence that the cluster comprises 7 magnetic Co ions. We argue that the doped hole couples these ions ferromagnetically yielding a spin-state polaron with a huge local magnetic moment.