Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 16: Posters Correlated Electrons, Measuring Devices, Cryotechnique

TT 16.9: Poster

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

Tuning the Spin-State and Insulator-Metal Transition in LaCoO₃ by Eu-Doping — •J. Baier, M. Kriener, S. Jodlauk, A. Reichl, C. Zobel, H. Kierspel, A. Freimuth, and T. Lorenz — II. Physikalisches Institut, Universität zu Köln

We present a study of the structure, the electric resistivity, the magnetic susceptibility, and the thermal expansion of La_1−xEu_xCoO₃ [1]. LaCoO₃ shows a temperature-induced spin-state transition around 100 K and a metal-insulator transition around 500 K. Partial substitution of La³⁺ by the smaller Eu³⁺ causes chemical pressure and leads to a drastic increase of the spin gap from about 190 K in LaCoO₃ to about 2000 K in EuCoO₃, so that the spin-state transition is shifted to much higher temperatures. A combined analysis of thermal expansion and susceptibility gives evidence that the spin-state transition has to be attributed to a population of a spin-triplet state, as is realized in the intermediate-spin state of Co³⁺. In contrast to the spin-state transition, the metal-insulator transition is shifted only moderately to higher temperatures with increasing Eu content, showing that the metal-insulator transition occurs independently from the spin-state distribution of the Co³⁺ ions. Around the metal-insulator transition the magnetic susceptibility shows a similar increase for all x and approaches a doping-independent value around 1000 K indicating that well above the metal-insulator transition the same spin state is approached for all x.

[1] Baier et al., cond-mat 0405680, appears in Phys. Rev. B

Supported by the DFG through SFB 608