Structural and Electronic Properties of Cobalt/Alumina Tunnel Junctions from First Principles

Authors

Ivan I. Oleinik, University of Oxford, Oxford, UKFollow
Evgeny Y. Tsymbal, University of Nebraska-LincolnFollow
David G. Pettifor, University of OxfordFollow

ORCID IDs

Tsymbal http://orcid.org/0000-0002-6728-5493

Document Type

Article

Date of this Version

3-2000

Citation

Physical Review B (2000) 62: 3,952-3,959

Comments

Copyright © 2000, American Physical Society. Used by permission

Abstract

A detailed first-principles study of the atomic and electronic structure of the Co/Al₂O₃/Co magnetic tunnel junction has been performed in order to elucidate the key features determining the spin-dependent tunneling. The atomic structure of the multilayer with the O- and Al-terminated interfaces between fcc Co(111) and crystalline α-Al₂O₃(0001) has been optimized using self-consistent spin-polarized calculations within densityfunctional theory and the generalized gradient approximation. We found that the relaxed atomic structure of the O-terminated interface is characterized by a rippling of the Co interfacial plane, the average Co-O bond length being 2.04 Å which is within 5% of that in bulk CoO. The corresponding electronic structure is influenced by the covalent bonding between the O 2p and Co 3d orbitals resulting in exchange-split bonding and antibonding states and an induced magnetic moment of 0.07 µ_B on the interfacial oxygen atoms. The Al-terminated interface contains Co-Al bonds with an average bond length of 2.49 Å compared to 2.48 Å in bulk CoAl. Due to charge transfer and screening effects the Co interfacial layer acquires a negative charge which results in a reduced magnetic moment of 1.15 µ_B per Co atom. We found that the electronic structure of the O-terminated Co/Al₂O₃/Co tunnel junction exhibits negative spin polarization at the Fermi energy within the first few monolayers of alumina but it eventually becomes positive for distances beyond 10 Å.