Thermal excitation of the Co3+ triplet spin-state in LaCoO3 determined by polarized neutron diffraction

The magnetic moment induced by an external magnetic field of 5.8 T on the Co3+ ions in LaCoO3 has been measured by polarized neutron diffraction. Measurements were made at 100 K, near to the susceptibility maximum usually associated with a gradual spin-state transition, as well as at 1.5 and at 285 K. The data give evidence for a transition from the ground singlet state (S = 0) to the excited triplet intermediate spin-state (S = 1). The energy of ΔH≈1000 K estimated for the high-spin-state (S = 2), is too high to make a significant contribution to the moment, even at T = 285 K. There is evidence for a small negative spin density associated with the oxygen ligands in agreement with the theory that predicts intermediate spin as the first excited state.