Regensburg 2002 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 22: Postersitzung III: Syst. korr. Elektr.: Theorie II (1-15), Metall-Isol.- und Phasenüberg
änge (16-33), SL: Massivmat., Bandl., Pinning, Vortexdyn., Transport, Korngr. (34-43), Niedrigdim. Syst., Magnetotransport (44-63)

TT 22.29: Poster

Donnerstag, 14. März 2002, 14:00–17:30, A

X-ray absorption study of the spin state transition in La1−xSrxCoO3 single crystals — •Z.-W. Hu1, M. Haverkort1, L.H. Tjeng1, S. Csiszar2, M. Kriener1, C. Zobel1, H. Kierspel1, T. Lorentz1, A. Freimuth1, H.-J. Lin3, H.-H. Hsieh3, and C.T. Chen31II. Physikalisches Institut, Universität zu Köln — 2University of Groningen, The Netherlands — 3SRRC, Hsinchu, Taiwan

We have studied the O 1s and the Co L23 XAS spectra of La1−xSrxCoO3 (x = 0, 0.01, 0.04, 0.125, 0.25) single crystals as a function of temperature from 20 K to 650 K. The low spin state of LaCoO3 at 20 K is confirmed by a comparison with EuCoO3. Upon increasing the temperature a clear increase in the intensity of a new pre-edge peak in the O 1s XAS spectrum of LaCoO3 indicates the increase in the population of the intermediate spin state with a jump at around 90 K. This observation clarifies the discrepancy between previous XAS and magnetic studies concerning the first magnetic transition at 90 K. Above 600 K this new feature becomes dominant. However, the spectrum is different from that of FeO, which has the well known high-spin state of 3d6. The significant difference between the Co L23 XAS of LaCoO3 and the Fe L23 XAS spectra of FeO is also observed. These results exclude the presence of a pure high-spin state at the second magnetic transition temperature around 500 K. In case of Sr doping, the observed spectral changes can be assigned to a combined effect of a spin-state transition and an increased presence of Co(IV) ions. The temperature effects on the spin-state transition extend to the ferromagnetic phase for x = 0.125.

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