Theory of orbital state and spin interactions in ferromagnetic titanates
- 24 November 2003
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review B
- Vol. 68 (20), 205109
- https://doi.org/10.1103/physrevb.68.205109
Abstract
A spin-orbital superexchange Hamiltonian in a Mott insulator with orbital degeneracy is investigated. More specifically, we focus on a spin ferromagnetic state of the model and study a collective behavior of orbital angular momentum. Orbital order in the model occurs in a nontrivial way—it is stabilized exclusively by quantum effects through the order-from-disorder mechanism. Several energetically equivalent orbital orderings are identified. Some of them are specified by a quadrupole ordering and have no unquenched angular momentum at low energy. Other states correspond to a noncollinear ordering of the orbital angular momentum and show the magnetic Bragg peaks at specific positions. Order parameters are unusually small because of strong quantum fluctuations. Orbital contribution to the resonant x-ray scattering is discussed. The dynamical magnetic structure factor in different ordered states is calculated. Predictions made should help to observe elementary excitations of orbitals and also to identify the type of the orbital order in ferromagnetic titanates. Including further a relativistic spin-orbital coupling, we derive an effective low-energy spin Hamiltonian and calculate a spin-wave spectrum, which is in good agreement with recent experimental observations in
Keywords
This publication has 29 references indexed in Scilit:
- Magnetic Order and Dynamics in an Orbitally Degenerate Ferromagnetic InsulatorPhysical Review Letters, 2002
- Spin Order due to Orbital Fluctuations: Cubic VanadatesPhysical Review Letters, 2001
- Orbital Liquid in Three-Dimensional Mott Insulator:Physical Review Letters, 2000
- Spin Dynamics and Orbital State inPhysical Review Letters, 2000
- Orbital Physics in Transition-Metal OxidesScience, 2000
- Metal-insulator transitionsReviews of Modern Physics, 1998
- Magnetic behavior in the series LaxY1−xTiO3Journal of Solid State Chemistry, 1982
- The Jahn-Teller effect and magnetism: transition metal compoundsSoviet Physics Uspekhi, 1982
- Superexchange interaction and symmetry properties of electron orbitalsJournal of Physics and Chemistry of Solids, 1959
- Theory of the Role of Covalence in the Perovskite-Type ManganitesPhysical Review B, 1955