Orbital order, anisotropic spin couplings, and the spin-wave spectrum of the ferromagnetic Mott insulator YTiO3

After discovering a subtle sign error in our previous work (Ann. Phys. (Leipzig) 14, 626 (2005)) we have redone our calculations of the superexchange couplings in the ferromagnetic Mott insulator YTiO3. In contrast to the earlier result, the corrected calculations give realistic ferromagnetic Heisenberg couplings for Ti-Ti bonds in the crystallographic ab planes as well as along the c direction. The calculated antisymmetric (Dzyaloshinskii-Moriya) and symmetric anisotropy terms of the superexchange Hamiltonian are also modified. Based on the calculated superexchange couplings we determine the magnetic order of the Ti ions and the spin-wave spectrum, and both are found in acceptable agreement with experiment. Our model, in which the orbital degrees of freedom are frozen by the crystal field, also reproduces the experimentally observed orbital ordering pattern of the Ti ions. Therefore, this model provides a consistent picture of the orbital and of the magnetic ordering mechanisms in YTiO3. These mechanisms are coupled together, and have been a subject of considerable debate. (Abstract Copyright [2007], Wiley Periodicals, Inc.)