Magnetic and Orbital States and Their Phase Transition of the Perovskite-Type Ti Oxides: Strong Coupling Approach

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The properties and mechanism of the magnetic phase transition of the perovskite-type Ti oxides, which is driven by the Ti-O-Ti bond angle distortion, are studied theoretically by using the effective spin and pseudospin Hamiltonian with strong Coulomb repulsion. It is shown that the A-type antiferromagnetic (AFM(A)) to ferromagnetic (FM) phase transition occurs as the Ti-O-Ti bond angle is decreased. Through this phase transition, the orbital state changes only little whereas the spin-exchange coupling along the c-axis is expected to change from positive to negative nearly continuously and approaches zero at the phase boundary. The resultant strong two-dimensionality in the spin coupling causes rapid suppression of the critical temperature, as observed experimentally. It may induce large quantum fluctuations in this region.

Original languageEnglish
Pages (from-to)1777-1789
Number of pages13
JournalJournal of the Physical Society of Japan
Issue number6
Publication statusPublished - 2001 Jun
Externally publishedYes



  • A-type antiferromagnetism
  • d-type Jahn-Teller distortion
  • GdFeO-type distortion
  • Mermin and Wagner's theorem
  • Orbital degrees of freedom
  • Orbital ordering
  • Perovskite-type Ti oxides
  • Second-order perturbation theory
  • Two-dimensional spin coupling

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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