Spin and Orbital States and Their Phase Transitions of the Perovskite-Type Ti Oxides: Weak coupling Approach

Abstract

The magnetic phase diagram of the perovskite-type Ti oxides as a function of the GdFeO3-type distortion is examined by using the Hartree-Fock analysis of a multiband d-p Hamiltonian from a viewpoint of competitions of the spin-orbit interaction, the Jahn-Teller (JT) level-splitting and spin-orbital superexchange interactions. Near the antiferromagnetic (AFM)-to-ferromagnetic (FM) phase boundary, A-type AFM [AFM(A)] and FM states accompanied by a certain type of orbital ordering are lowered in energy at large JT distortion, which is in agreement with the previous strong coupling study. With increasing the GdFeO3-type distortion, their phase transition occurs. Through this magnetic phase transition, the orbital state hardly changes, which induces nearly continuous change in the spin coupling along the c-axis from negative to positive. The resultant strong two-dimensionality in the spin coupling near the phase boundary is attributed to the strong suppression of T_N and T_C, which is experimentally observed. On the other hand, at small GdFeO3-type without JT distortions, which correspond to LaTiO3, the most stable solution is not G-type AFM [AFM(G)] but FM. Although the spin-orbit interaction has been considered to be relevant at the small or no JT distortion of LaTiO3 in the literature, our analysis indicates that the spin-orbit interaction is irrelevant to the AFM(G) state in LaTiO3 and superexchange-type interaction dominates. On the basis of further investigations on the nature of this FM state and other solutions, this discrepancy is discussed in detail.

arXiv comment9 pages, 10 figures

References in corpus (6)

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• Magnetic and Metal-Insulator Transitions through Bandwidth Control in Two-Dimensional Hubbard Models with Nearest and Next-Nearest Neighbor Transfers
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• Dipole-active optical phonons in YTiO_3: ellipsometry study and lattice-dynamics calculations
• Fingerprints of spin-orbital polarons and of their disorder in the photoemission spectra of doped Mott insulators with orbital degeneracy
• Orbital order, anisotropic spin couplings, and the spin-wave spectrum of the ferromagnetic Mott insulator YTiO3
• On the Neglect of Local Coulomb Interaction on Oxygens in Perovskites Described by the Multi-band $d-p$ Model
• Electronic reconstruction in correlated electron heterostructures