Temperature 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 spin-state transition, at 1.5 K 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 K estimated for the high-spin (S = 2) state, is too high to contribute significantly even at T = 285 K. There is evidence for a small negative covalent spin density associated with the oxygen ligands amounting to about one fifth of the aligned Co3+ moment at all three temperatures. 
V.P.Plakhty, P.J.Brown, B.Grenier, S.V.Shiryaev, S.N.Barilo, S.V.   Gavrilov, E.Ressouche