Article

Spontaneous exchange bias formation driven by a structural phase transition in the antiferromagnetic material

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Abstract

Most of the magnetic devices in advanced electronics rely on the exchange bias effect, a magnetic interaction that couples a ferromagnetic and an antiferromagnetic material, resulting in a unidirectional displacement of the ferromagnetic hysteresis loop by an amount called the ‘exchange bias field’. Setting and optimizing exchange bias involves cooling through the Néel temperature of the antiferromagnetic material in the presence of a magnetic field. Here we demonstrate an alternative process for the generation of exchange bias. In IrMn/FeCo bilayers, a structural phase transition in the IrMn layer develops at room temperature, exchange biasing the FeCo layer as it propagates. Once the process is completed, the IrMn layer contains very large single-crystal grains, with a large density of structural defects within each grain, which are promoted by the FeCo layer. The magnetic characterization indicates that these structural defects in the antiferromagnetic layer are behind the resulting large value of the exchange bias field and its good thermal stability. This mechanism for establishing the exchange bias in such a system can contribute towards the clarification of fundamental aspects of this exchange interaction.

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Acknowledgements

We thank K. O’Grady for his helpful discussions. This work has been funded by the Spanish Ministerio de Economía y Competitividad through the projects MAT2014-52477-C5-1-P and MAT2014-52477-C5-3-P and by the Spanish Consejo Social of the Universidad Politécnica de Madrid through the scholarship ‘Ayuda del Consejo Social para el Fomento de la formación y la Internacionalización de Doctorandos’, awarded for a three months internship at the University of York. V.K.L. thanks the funding support by EPSRC grant EP/K03278X/1. J.C. and J.L.F.C. thank support by MINECO through Projects FIS2016-78591-C3-1-R and SEV-2016-0686 and by Comunidad de Madrid through Project S2013/MIT-2850.

Author information

Affiliations

  1. Instituto de Sistemas Optoelectrónicos y Microtecnología-ISOM. Universidad Politécnica de Madrid, Avenida Complutense 30, 28040 Madrid, Spain

    • A. Migliorini
    • , C. Aroca
    •  & J. L. Prieto
  2. Department of Physics, University of York, York YO10 5DD, UK

    • B. Kuerbanjiang
    • , T. Huminiuc
    • , G. Vallejo-Fernández
    •  & V. K. Lazarov
  3. SuperSTEM, STFC Daresbury Laboratories, Keckwick Lane, Warrington WA4 4AD, UK

    • D. Kepaptsoglou
  4. IMN-Instituto de Micro y Nanotecnología, (CNM-CSIC), Isaac Newton 8, 28760 Tres Cantos, Madrid, Spain

    • M. Muñoz
  5. IMDEA-Nanoscience, c/ Faraday, 9 Campus de Cantoblanco, 28049 Madrid, Spain

    • J. L. F. Cuñado
    •  & J. Camarero
  6. DFMC and Instituto “Nicolás Cabrera”, Universidad Autónoma de Madrid, 28049 Madrid, Spain

    • J. L. F. Cuñado
    •  & J. Camarero
  7. Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, 28049 Madrid, Spain

    • J. Camarero

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Contributions

A.M. deposited the samples and performed (or was strongly involved) in most of the experimental characterization. T.H. performed some of the crystallization experiments observed using electron microscopy. M.M. designed some of the experimental set-ups used for characterizations. J.L.F.C. and J.C. provided expertise and performed Kerr microscopy with A.M. C.A. was the first to suggest that a phase transition in the IrMn was probably behind the unusual behaviour of the samples. G.V.-F. helped with the magnetic characterization following the York protocol and performed the fitting displayed in Fig. 4d. V.K.L. and B.K. performed the TEM characterization with some of the specimens measured by D.K. J.L.P. directed the research and designed the sputtering system used for the deposition of the samples. J.L.P. wrote the manuscript with inputs from all the authors.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to J. L. Prieto.

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