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

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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 strong suppression of TN and TC, which is experimentally observed is attributed to the resulting strong two-dimensionality in the spin coupling near the phase boundary. 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.

Original languageEnglish
Pages (from-to)2039-2047
Number of pages9
Journaljournal of the physical society of japan
Volume71
Issue number8
DOIs
Publication statusPublished - 2002 Aug 1
Externally publishedYes

Keywords

  • GdFeO-type distortion
  • Multiband d-p model
  • Perovskite-type Ti oxides
  • Spin-orbit interaction
  • d-level degeneracy
  • d-type Jahn-Teller distortion

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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