Dresden 2009 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 29: Correlated Electrons: Low-dimensional Systems - Materials 2

TT 29.10: Vortrag

Mittwoch, 25. März 2009, 16:30–16:45, HSZ 301

Spin-state polaron in lightly hole doped LaCoO₃ — •A. Alfonsov¹, E. Vavilova^1,2, V. Kataev¹, 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

LaCoO₃ is nonmagnetic at low temperatures and shows a T-activated magnetism due to a change of the Co³⁺ spin state. Surprisingly, a very small Sr²⁺ (i.e. hole) doping yields a strong magnetic response already at low T. To establish its nature we performed electron spin- (ESR), nuclear magnetic resonance (NMR) and inelastic neutron scattering (INS) measurements of lightly doped La_1−xSr_xCoO₃ single crystals (x∼ 0.002). ⁵⁹Co NMR data indicate the formation of extended magnetic clusters distributed over the entire sample volume. Low-T ESR spectra show up multiple lines with large g-factors suggesting that these clusters have a large spin multiplicity with a strong orbital contribution. From the Q-dependence of the INS intensity we conclude that the cluster comprises 7 magnetic Co ions. We propose a mechanism of how already a very light hole doping yields a formation of big spin polarons in LaCoO₃.