Effect of light Sr doping on the spin-state transition in LaCoO_3

TL;DR

This study uses neutron scattering to investigate how light Sr doping affects the spin-state transitions in LaCoO_3, revealing new low-energy excitations and supporting the formation of magnetic polarons.

Contribution

It provides new insights into the spin-state transitions induced by light Sr doping in LaCoO_3 using inelastic neutron scattering.

Findings

Discovery of a low-energy inelastic peak at ~0.75 meV below 30 K.

Observation of a thermally induced spin-state transition starting above 30 K.

Evidence suggesting hole doping creates magnetic polarons leading to spin-state changes.

Abstract

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.