Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 16: Posters Correlated Electrons, Measuring Devices, Cryotechnique

TT 16.46: Poster

Samstag, 5. März 2005, 11:00–16:30, Poster TU C

Transport and Thermodynamic Properties of RCoO₃, R= La, Pr, Nd and Eu — •M. Kriener, K. Berggold, J. B aier, S. Jodlauk, H. Kierspel, T. Lorenz, M. Reuther, C. Zobel, and A. Freimuth — II. Physikalisches Institut, Universität zu Köln, 50937 Köln

LaCoO₃ is an insulator with unusual magnetic properties. Around 100 K LaCoO₃ shows a temperature-induced spin-state transition from a nonmagnetic low-spin state (electronic configuration of the Co³⁺-ions: t_2g⁶e_g⁰ with S = 0) to an intermediate-spin state (t_2g⁵e_g¹ with S = 1) [1]. Around 500 K a metal-insulator transition occurs. The spin state of Co³⁺ is determined by the balance of crystal-field splitting and Hund’s rule coupling. We have studied the influence of an enhanced crystal field by substituting the La³⁺ ions by smaller isovalent rare-earth ions. Our study of the magnetic susceptibility, the thermal expansion and the electrical resistivity shows that Eu-doping causes a strong shift of the spin-state transition to higher temperatures, whereas the metal-insulator transition temperature increases only moderately [2]. Moreover, at low temperatures the thermal conductivity is strongly suppressed due to the spin-state transition in LaCoO₃. Replacing La completely by R= Pr, Nd or Eu systematically increases the thermal conductivity with decreasing radius of R, because of the shift of the spin-state transition towards higher temperatures.

[1] C. Zobel et al., Phys. Rev. B 66, 020402(R) (2002)

[2] J. Baier et al., appears in Phys. Rev. B, cond-mat 0405680 (2004) Supported by the DFG through SFB 608.