Eur. Phys. J. B 17, 103-109 (2000)
https://doi.org/10.1007/s100510070164

Stabilization of A-type layered antiferromagnetic phase in LaMnO₃ by cooperative Jahn-Teller deformations

¹ Istituto Nazionale di Fisica della Materia and International School for Advanced Studies (SISSA-ISAS), Via Beirut 2-4, 34013 Trieste, Italy
² Laboratoire d'Études des Propriétés Électroniques des Solides, CNRS, associated with Université Joseph Fourier, BP 166, 38042 Grenoble Cedex 9, France
³ Istituto Nazionale di Fisica della Materia and Dipartimento di Fisica, Università di Roma "La Sapienza", Piazzale Aldo Moro 2, 00185 Roma, Italy

Received: 24 January 2000
Published online: 15 September 2000

Abstract

It is shown that the layered antiferromagnetic order in stoechiometric LaMnO₃ 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 Q₃ < 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 e_g and t_2g 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 (Q₃ > 0). The crucial role of the deformation anisotropy is also emphasized.