Origin of the Antiferroorbital Ordering in LaMnO_3 and Other Related Compounds (Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

概要

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In order to get a realistic view of the origin of the antiferroorbital (AFO) order in LaMnO_3, MnF_3 and KCuF_3, both the cooperative Jahn-Teller effect (CJTE) and the orbital-dependent exchange interaction (OEI) are taken into account for the dγ electron-lattice system in compounds with the perovskite-type structure. The phonon-mediated orbital interaction in the CJTE and the dγ electron-mediated one in the OEI are treated by use of the mean-field approximation with preserving the symmetry of the crystal, and are joined to give an effective Hamiltonian. It is stressed that the CJTE favors any of the FO and AFO orders, while the OEI does only the AFO order. The present theory is consistent with the observed fact that the AFO order is characterized by an arrangement of alternate mixed orbitals of d_<x^2-y^2> and d_<3z^2-r^2>, the AFO phase survives even at sufficiently high temperatures in the paramagnetic phase, and the AFO order is always accompanied by the ferrodistortion and the antiferrodistortion.
社団法人日本物理学会の論文
2004-05-15