Magnetism of LaAlO₃/SrTiO₃ superlattices

Authors

Karolina Janicka, University of Nebraska - Lincoln
Julian P. Velev, University of Nebraska-LincolnFollow
Evgeny Y. Tsymbal, University of Nebraska-LincolnFollow

Date of this Version

1-31-2008

Comments

Published in JOURNAL OF APPLIED PHYSICS 103, 07B508 (2008). Copyright © 2008 American Institute of Physics. Used by permission.

Abstract

First-principles electronic structure calculations are performed to elucidate magnetic properties of LaAlO₃ /SrTiO₃ heterostructures. We find that TiO₂-terminated interfaces are n-type conducting which is consistent with experimental observations. In a (LaAlO₃ ) ₃ / (SrTiO₃)₃ superlattice, this interface is magnetic with a magnetic moment on the Ti³⁺ atom of 0.2 μ_B, as revealed by the spin-polarized calculations within the local density approximation (LDA). For thicker SrTiO₃ layers the magnetic moment decreases and eventually disappears because the electron gas spreads over more than one unit cell, making the electron delocalized across the superlattice and violating the Stoner criterion for magnetism. Thus, magnetization in these superlattices is due to geometric confinement of the electron gas. The inclusion of electron correlations via the LDA+U approximation with U=5 eV on the Ti atoms makes the two-dimensional electron gas half-metallic and enhances and stabilizes the interface magnetization.