TY - JOUR
T1 - Magnetic and Orbital States and Their Phase Transition of the Perovskite-Type Ti Oxides
T2 - Strong Coupling Approach
AU - Mochizuki, Masahito
AU - Imada, Masatoshi
PY - 2001/6
Y1 - 2001/6
N2 - 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.
AB - 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.
KW - A-type antiferromagnetism
KW - GdFeO-type distortion
KW - Mermin and Wagner's theorem
KW - Orbital degrees of freedom
KW - Orbital ordering
KW - Perovskite-type Ti oxides
KW - Second-order perturbation theory
KW - Two-dimensional spin coupling
KW - d-type Jahn-Teller distortion
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U2 - 10.1143/JPSJ.70.1777
DO - 10.1143/JPSJ.70.1777
M3 - Article
AN - SCOPUS:0035612354
SN - 0031-9015
VL - 70
SP - 1777
EP - 1789
JO - Journal of the Physical Society of Japan
JF - Journal of the Physical Society of Japan
IS - 6
ER -