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Nano-crystal domain structures formed in a MgO barrier and their effects on tunnel magnetoresistance (TMR) in epitaxial fcc-Co90Fe10 (CoFe)(111)/MgO(111)/CoFe(111) magnetic tunnel junctions (MTJs) have been systematically studied using scanning transmission electron microscopy and first-principles calculations. These domains are widely distributed in the (111)-textured MgO layer, being different from conventional bcc-CoFe/MgO(001)-based MTJs. The (111)-texture is formed by extension of {111} planes through several adjacent MgO domains. Three types of orientation relationships (ORs) between CoFe and MgO are identified, including cube-on-cube type (Type-1), twin-like type (Type-2), and unexpected type (Type-3). Crystallographic analysis indicated that Type-2 OR is a variant of Type-1 OR, triggered by different stacking orders of MgO(111) planes, while Type-3 OR is formed by a 30◦ in-plane rotation of MgO lattice relative to Type-1 OR. Due to the large in-plane lattice mismatch (19.6%) between Co(111) and MgO(111) in Type-1 and Type-2 ORs, Type-3 OR (mismatch 3.4%) can be stabilized. First-principles calculations uncovered that the theoretical TMR ratio of the MgO(111) MTJ with Type-3 OR is ~2 orders of magnitude smaller than that with Type-1 and Type-2 ORs. The small contribution of Type-3 OR to the transport reasonably interprets why the experimental TMR ratio (~37%) is much lower than the theoretical value (~2100%) in the Co/MgO/Co(111) MTJ. This study has revealed the nano-crystal domain formation unique to the fcc-CoFe/MgO(111) MTJs, indicating that controlling the nano-crystal domains (e.g., lattice optimization by atomic doping) can be a guiding principle to develop MgO(111)-based epitaxial MTJs and related heterostructure devices.

Rights:

• Creative Commons BY-NC-ND Attribution-NonCommercial-NoDerivs 4.0 International
  

Keyword: Spintronics, Magnetic tunnel junctions, Tunnel magnetoresistance, Epitaxial growth

Date published: 2023-09-27

Publisher: Elsevier BV

Journal:

• Acta Materialia (ISSN: 13596454) vol. 261 119394

Funding:

• Japan Society for the Promotion of Science 20K14782
• Japan Society for the Promotion of Science 22H04966
• Japan Society for the Promotion of Science 23K03933
• Core Research for Evolutional Science and Technology
• Japan Science and Technology Agency Strategic Basic Research Programs CREST JPMJCR19J4
• Japan Society for the Promotion of Science 21H01750

Manuscript type: Author's version (Accepted manuscript)

MDR DOI: https://doi.org/10.48505/nims.4752

First published URL: https://doi.org/10.1016/j.actamat.2023.119394

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Updated at: 2025-10-21 16:16:53 +0900

Published on MDR: 2025-10-21 16:16:02 +0900