Origin of G-type antiferromagnetism and orbital-spin structures in LaTiO3

The possibility of the D-3d distortion of TiO6 octahedra is examined theore tically in order to understand tile origin of the G-type antiferromagnetism [AFM(G)] and experiment ally observed puzzling properties of LaTiO3. By ut ilizing an effective spin and pseudospin Hamiltonian with the strong Coulom b repulsion, it is shown that tile AFM(G) state is stabilized through the l ift of the t(2g)-orbital degeneracy accompanied by a tiny D-3d-distortion. The estimated spin-exchange interaction is in agreement with that obtained by the neutron-scattering experiment. Moreover, the level-splitting energy due to the distortion can be considerably larger than the, pin-orbit intera ction even when the distortion becomes smaller than the detectable limit un der the available experimental resolution. This suggests that the orbital m omentum is fully quenched and tile relativistic spin-orbit interaction is n ot effective in this system, in agreement with the result of a recent neutr on-scattering experiment.