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

Abstract

Using a point-charge calculation of the electrostatic crystal field, we determine the non-degenerate orbital ground state of the ferromagnetic Mott insulator YTiO3, which is found to agree perfectly with experiment. Based on the orbital order, we obtain by perturbation theory an effective spin Hamiltonian that describes the magnetic superexchange between nearest-neighbor Ti ions. The superexchange Hamiltonian includes, in addition to the isotropic Heisenberg coupling, antisymmetric (Dzyaloshinskii-Moriya) and symmetric anisotropy terms, caused by the spin-orbit interaction on the Ti ions. We find ferromagnetic Heisenberg couplings for Ti-Ti bonds in the crystallographic ab planes, but antiferromagnetic ones for Ti-Ti bonds between planes, in contradiction with experiment (which gives ferromagnetic couplings for both). Difficulties in calculating realistic values for the isotropic couplings of YTiO3 have been already reported in the literature. We discuss possible origins for these discrepancies. However, the much smaller values we obtain for the symmetric and antisymmetric anisotropies may be expected to be reliable. We therefore combine the experimentally-deduced isotropic coupling with the calculated anisotropic ones to determine the magnetic order of the Ti ions, which is found to be in satisfactory agreement with experiment. Based on this magnetic order, we derive the spin-wave spectrum. We find an acoustic branch with a very small zone-center gap and three optical spin-wave modes with sizeable zone-center gaps. The acoustic branch reproduces the one reported in experiment, and the optical ones are in a satisfactory agreement with experiment, upon a proper folding of the magnetic Brillouin zone.

arXiv comment13 pages, 5 figures, submitted to Ann. Phys. Leipzig

References in corpus (12)

• Crystal and magnetic structure of LaTiO3 : evidence for non-degenerate $t_{2g}$-orbitals
• Spin Dynamics and Orbital State in LaTiO_3
• Orbital Physics in the Perovskite Ti Oxides
• Magnetic Order and Dynamics in an Orbitally Degenerate Ferromagnetic Insulator
• Orbital-Spin Structure and Coupling to Lattice in RTiO${}_3$ with R=La,Pr,Nd and Sm
• Lattice Distortion and Magnetic Ground State of YTiO${}_3$ and LaTiO${}_3$
• The magnetic structure of the Jahn-Teller System LaTiO3
• Structural distortions and orbital ordering in LaTiO3 and YTiO3
• Magnetic and Orbital States and Their Phase Transition of the Perovskite-Type Ti Oxides: Strong Coupling Approach
• Spin and Orbital States and Their Phase Transitions of the Perovskite-Type Ti Oxides: Weak coupling Approach
• The spin-wave spectrum of the Jahn-Teller system LaTiO3
• Orbital order, anisotropic spin couplings, and the spin-wave spectrum of the ferromagnetic Mott insulator YTiO3

Cited by in corpus (5)

• Cooperative Effect of Electron Correlation and Spin-Orbit Coupling on the Electronic and Magnetic Properties of Ba2NaOsO6
• Momentum dependence of orbital excitations in Mott-insulating titanates
• Mott-Hubbard exciton in the optical conductivity of YTiO3 and SmTiO3
• Orbital order, anisotropic spin couplings, and the spin-wave spectrum of the ferromagnetic Mott insulator YTiO3
• Magnetic resonance as an orbital state probe