Stabilization of A-type layered antiferromagnetic phase in LaMnO3 by cooperative Jahn-Teller deformations |
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| Authors: | M Capone D Feinberg M Grilli |
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| Institution: | (1) Istituto Nazionale di Fisica della Materia and International School for Advanced Studies (SISSA-ISAS), Via Beirut 2-4, 34013 Trieste, Italy, IT;(2) Laboratoire d'études des Propriétés électroniques des Solides, CNRS, associated with Université Joseph Fourier, BP 166, 38042 Grenoble Cedex 9, France, FR;(3) Istituto Nazionale di Fisica della Materia and Dipartimento di Fisica, Università di Roma “La Sapienza", Piazzale Aldo Moro 2, 00185 Roma, Italy, IT |
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| 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.
Received 24 January 2000 |
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| Keywords: | PACS 71 70 Ej Spin-orbit coupling Zeeman and Stark splitting Jahn-Teller effect - 75 30 Et Exchange and superexchange interactions |
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