G-type Antiferromagnetism and Orbital Ordering due to the Crystal Field from the Rare-Earth Ions Induced by the GdFeO3-type Distortion in RTiO3 Where R=La, Pr, Nd and Sm

Mochizuki Masahito, Imada Masatoshi

doi:10.48550/arxiv.cond-mat/0312244

The origin of the antiferromagnetic order and puzzling properties of LaTiO₃ as well as the magnetic phase diagram of the perovskite titanates are studied theoretically. We show that in LaTiO₃, the t_2g degeneracy is eventually lifted by the La cations in the GdFeO₃-type structure, which generates a crystal field. This allows the description of the low-energy structure of LaTiO₃ 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 LaTiO₃ obtained by the neutron scattering experiment. The orbital-spin structures for RTiO₃ where R=Pr, Nd and Sm are also accounted for by the same mechanism. We point out that through generating the R crystal field, the GdFeO₃-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 GdFeO₃-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.

G-type Antiferromagnetism and Orbital Ordering due to the Crystal Field from the Rare-Earth Ions Induced by the GdFeO<SUB>3</SUB>-type Distortion in <I>R</I>TiO<SUB>3</SUB> Where <I>R</I>=La, Pr, Nd and Sm

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