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Exchange bias of the interface spin system at the Fe/MgO interface

Nature Nanotechnology volume 8, pages 438–444 (2013)Cite this article

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Abstract

The ferromagnet/oxide interface is key to developing emerging multiferroic and spintronic technologies with new functionality. Here we probe the Fe/MgO interface magnetization, and identify a new exchange bias phenomenon manifested only in the interface spin system, and not in the bulk. The interface magnetization exhibits a pronounced exchange bias, and the hysteresis loop is shifted entirely to one side of the zero field axis. However, the bulk magnetization does not, in marked contrast to typical systems where exchange bias is manifested in the net magnetization. This reveals the existence of an antiferromagnetic exchange pinning layer at the interface, identified here as FeO patches that exist even for a nominally ‘clean’ interface. These results demonstrate that atomic moments at the interface are non-collinear with the bulk magnetization, and therefore may affect the net anisotropy or serve as spin scattering sites. We control the exchange bias magnitude by varying the interface oxygen concentration and Fe–O bonding.

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Figure 1: Model of TMR structure and of atomic moments near the Fe/MgO interface.
Figure 2: Measurement geometry and MOKE/MSHG data.
Figure 3: Classic model of exchange bias.
Figure 4: TEM images of sample interfaces.
Figure 5: Magnitude of exchange bias field HE versus applied field direction.
Figure 6: Temperature dependence of the exchange bias.

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Acknowledgements

The work at College of William and Mary was supported by the Office of Naval Research. The work at NRL was supported by core programmes and the Office of Naval Research. The work at Fudan University was supported by the Natural Science Foundation of China (grant nos 61222407 and 11074044).

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Author notes

  1. Y. Fan

    Present address: Present address: Seagate Technology, 1200 Disc Drive, Shakopee, Minnesota 55379, USA,

Authors and Affiliations

  1. Department of Applied Science, College of William and Mary, 251 Jamestown Road, Williamsburg, 23187, Virginia, USA

    Y. Fan, K. J. Smith & G. Lüpke

  2. Materials Science and Technology Division, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375, USA

    A. T. Hanbicki, R. Goswami, C. H. Li & B. T. Jonker

  3. Department of Optical Science and Engineering, Fudan University, 220 Handan Road, Shanghai, 200433, China

    H. B. Zhao

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Contributions

Y.F., G.L. and B.T.J. conceived the experiment. A.T.H. and C.L. grew the samples and carried out magnetic characterization using vibrating sample magnetometry. R.G. performed the TEM measurements. Y.F. performed the MSHG and MOKE measurements. All authors contributed to interpretation of the data. Y.F., K.J.S., G.L. and B.T.J. wrote the manuscript.

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Correspondence to G. Lüpke or B. T. Jonker.

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Fan, Y., Smith, K., Lüpke, G. et al. Exchange bias of the interface spin system at the Fe/MgO interface. Nature Nanotech 8, 438–444 (2013). https://doi.org/10.1038/nnano.2013.94

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