G-type antiferromagnetism and orbital ordering due to the crystal field from the rare-earth ions induced by the GdFeO_3-type distortion in RTiO_3 with R=La, Pr, Nd and Sm

Abstract

The origin of the antiferromagnetic order and puzzling properties of LaTiO_3 as well as the magnetic phase diagram of the perovskite titanates are studied theoretically. We show that in LaTiO_3, the t_{2g} degeneracy is eventually lifted by the La cations in the GdFeO_3-type structure, which generates a crystal field with nearly trigonal symmetry. This allows the description of the low-energy structure of LaTiO_3 by a single-band Hubbard model as a good starting point. The lowest-orbital occupation in this crystal field stabilizes the AFM(G) state, and well explains the spin-wave spectrum of LaTiO_3 obtained by the neutron scattering experiment. The orbital-spin structures for RTiO_3 with R=Pr, Nd and Sm are also accounted for by the same mechanism. We point out that through generating the R crystal field, the GdFeO_3-type distortion has a universal relevance in determining the orbital-spin structure of the perovskite compounds in competition with the Jahn-Teller mechanism, which has been overlooked in the literature. Since the GdFeO_3-type distortion is a universal phenomenon as is seen in a large number of perovskite compounds, this mechanism may also play important roles in other compounds of this type.

arXiv comment20 pages, 15 figures

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• Mott-Hubbard exciton in the optical conductivity of YTiO3 and SmTiO3
• Floquet engineering of multi-orbital Mott insulators: applications to orthorhombic titanates
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• Structural and metal-insulator transitions in rhenium based double perovskites via orbital ordering
• Pressure-driven orbital reorientation and change in Mott-Hubbard gap in YTiO3
• Orbital and spin order in oxide two-dimensional electron gases
• On the Neglect of Local Coulomb Interaction on Oxygens in Perovskites Described by the Multi-band $d-p$ Model
• Magnetic resonance study of rare-earth titanates