Effect of light Sr doping on the spin-state transition in LaCoO3

We present an inelastic neutron scattering study of the low energy crystal-field excitations in the lightly doped cobalt perovskite La0.998Sr0.002CoO3. In contrast to the parent compound LaCoO3 an inelastic peak at energy transfer similar to 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 similar to 0.6 meV was found at intermediate temperatures starting from T > 30K. This confirms the presence of a thermally induced spin-state transition from the low-spin Co3+ to a magnetic high-spin state in the non-disturbed LaCoO3 matrix. We suggest that hole doping of LaCoO3 leads to the creation of a magnetic polaron and hence to the low-to-high spin state transition on the relevant Co sites. (c) 2006 Elsevier B.V. All rights reserved.