Jahn-Teller distortions and the magnetic order in the perovskite manganites

Krzysztof Rościszewski; Andrzej M. Oleś

doi:10.1088/0953-8984/22/42/425601

paper

Jahn-Teller distortions and the magnetic order in the perovskite manganites

arXiv:1010.4982 · doi:10.1088/0953-8984/22/42/425601

Abstract

We introduce an effective model for $e_{g}$ electrons to describe three-dimensional perovskite (La $_{1 - x}$ Sr $_{x}$ MnO $_{3}$ and La $_{1 - x}$ Ca $_{x}$ MnO $_{3}$ ) manganites and study the magnetic and orbital order on $4 \times 4 \times 4$ cluster using correlated wave functions. The model includes the kinetic energy, and on-site Coulomb interactions for $e_{g}$ electrons, antiferromagnetic superexchange interaction between $S = 3/2$ core spins, and the coupling between $e_{g}$ electrons and Jahn-Teller modes. The model reproduces the experimentally observed magnetic order: ( $i$ ) $A$ -type antiferromagnetic phase in the undoped insulator LaMnO $_{3}$ , with alternating $e_{g}$ orbitals and with small Jahn-Teller distortions, changing to a conducting phase at 32 GPa pressure, and ( $ii$ ) ferromagnetic order in one-eight doped La $_{7/8}$ Sr $_{1/8}$ MnO $_{3}$ and in quarter doped La $_{3/4}$ Sr $_{1/4}$ MnO $_{3}$ compounds. For half-doped La $_{1/2}$ Ca $_{1/2}$ MnO $_{3}$ one finds a competition between a ferromagnetic conductor and the CE insulating phase; the latter is stabilized by the Jahn-Teller coupling being twice larger than for the strontium-doped compound. Altogether, there is a subtle balance between all Hamiltonian parameters and the phase diagram is quite sensitive to the precise values they take.

16 pages, 6 figures

Jahn-Teller distortions and the magnetic order in the perovskite manganites

Abstract

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