Effects of strain on orbital ordering and magnetism at perovskite oxide interfaces: LaMnO3/SrMnO3

B. R. K. Nanda and Sashi Satpathy
Phys. Rev. B 78, 054427 – Published 19 August 2008

Abstract

We study how strain affects orbital ordering and magnetism at the interface between SrMnO3 and LaMnO3 from density-functional calculations and interpret the basic results in terms of a three-site Mn-O-Mn model. Magnetic interaction between the Mn atoms is governed by a competition between the antiferromagnetic superexchange of the Mnt2g core spins and the ferromagnetic double exchange of the itinerant eg electrons. While the core electrons are relatively unaffected by the strain, the orbital character of the itinerant electron is strongly affected, which in turn causes a large change in the strength of the ferromagnetic double exchange. The epitaxial strain produces the tetragonal distortion of the MnO6 octahedron, splitting the Mneg states into x2y2 and 3z21 states, with the former being lower in energy, if the strain is tensile in the plane and opposite if the strain is compressive. For the case of the tensile strain, the resulting higher occupancy of the x2y2 orbital enhances the in-plane ferromagnetic double exchange owing to the larger electron hopping in the plane, causing at the same time a reduction in the out-of-plane double exchange. This reduction is large enough to be overcome by antiferromagnetic superexchange, which wins to produce a net antiferromagnetic interaction between the out-of-plane Mn atoms. For the case of the in-plane compressive strain, the reverse happens, viz., that the higher occupancy of the 3z21 orbital results in the out-of-plane ferromagnetic interaction, while the in-plane magnetic interaction remains antiferromagnetic. Concrete density-functional results are presented for the (LaMnO3)1/(SrMnO3)1 and (LaMnO3)1/(SrMnO3)3 superlattices for various strain conditions.

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  • Received 31 March 2008

DOI:https://doi.org/10.1103/PhysRevB.78.054427

©2008 American Physical Society

Authors & Affiliations

B. R. K. Nanda and Sashi Satpathy

  • Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, USA

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Issue

Vol. 78, Iss. 5 — 1 August 2008

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