Effect of light Sr doping on the spin–state transition in [formula omitted

Abstract

We present an inelastic neutron scattering study of the low energy crystal-field excitations in the lightly doped cobalt perovskite La 0.998 Sr 0.002 CoO 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.