We present an inelastic neutron scattering study of the low energy crystal-field excitations in the lightly doped cobalt perovskite La_0.998Sr_0.002CoO_3. In contrast to the parent compound LaCoO_3 an inelastic peak at energy transfer ~0.75 meV was found at temperatures below 30 K. This excitation apparently corresponds to a transition between a ground state orbital singlet and a higher excited orbital doublet, originating from a high-spin triplet split by a small trigonal crystal field. Another inelastic peak at an energy transfer ~0.6 meV was found at intermediate temperatures starting from T > 30 K. This confirms the presence of a thermally induced spin-state transition from the low-spin Co^3+ to a magnetic high-spin state in the non-disturbed LaCoO_3 matrix. We suggest that hole doping of LaCoO_3 leads to the creation of a magnetic polaron and hence to the low-to-high spin state transition on the relevant Co sites.
@article{arxiv.cond-mat/0609247,
title = {Effect of light Sr doping on the spin-state transition in LaCoO_3},
author = {A. Podlesnyak and K. Conder and E. Pomjakushina and A. Mirmelstein and P. Allenspach and D. I. Khomskii},
journal= {arXiv preprint arXiv:cond-mat/0609247},
year = {2008}
}
Comments
4 pages, 2 figures; based on a talk given at ICM'06, Kyoto; to appear in JMMM