Stabilization of A-type layered antiferromagnetic phase in LaMnO by cooperative Jahn-Teller deformations

1434-6036

PACS. 71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect - 75.30.Et Exchange and superexchange interactions

Springer Online Journal Archives 1860-2000

Physics

Abstract: It is shown that the layered antiferromagnetic order in stoechiometric cannot be understood purely from electronic interactions. On the contrary, it mainly results from strong cooperative Jahn-Teller deformation. Those involve a compression of the Mn-O octahedron along the c-axis (mode Q 3 〈 0), while alternate Jahn-Teller deformations occur in the ab-plane (mode Q2). These deformations stabilize a certain type of orbital ordering. The resulting superexchange couplings are calculated by exact diagonalization, taking into account both eg and t2g orbitals. The main result is that antiferromagnetic (ferromagnetic) coupling along the c-direction (ab-planes) can be understood only if the Jahn-Teller energy is much larger than the superexchange couplings, which is consistent with experiments. This mechanism contrasts with that based on weak Jahn-Teller coupling which instead predicts elongation along the c-axis (Q 3 〉 0). The crucial role of the deformation anisotropy is also emphasized.

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