We present measurements of the magnetic susceptibility and of the thermal expansion of a LaCoO3 single crystal. Both quantities show a strongly anomalous temperature dependence. Our data are consistently described in terms of a spin-state transition of the Co3+ ions with increasing temperature from a low-spin ground state to an intermediate-spin state without (100K - 500K) and with (>500K) orbital degeneracy. We attribute the lack of orbital degeneracy up to 500K to (probably local) Jahn-Teller distortions of the CoO6 octahedra. A strong reduction or disappearance of the Jahn-Teller distortions seems to arise from the insulator-to-metal transition around 500 K.
@article{arxiv.cond-mat/0205479,
title = {Evidence for a Low-Spin to Intermediate-Spin State Transition in LaCoO3},
author = {C. Zobel and M. Kriener and D. Bruns and J. Baier and M. Gr"uninger and T. Lorenz and P. Reutler and A. Revcolevschi},
journal= {arXiv preprint arXiv:cond-mat/0205479},
year = {2009}
}
Comments
an error in the scaling factor of Eq.(4) and consequently 2 values of table I have been corrected. The conclusions of the paper remain unchanged. See also: C. Zobel et al. Phys. Rev. B 71, 019902 (2005) and J. Baier et al. Phys. Rev. B 71, 014443 (2005)