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Full bulk spin polarization and intrinsic tunnel barriers at the surface of layered manganites

Nature Materials volume 4, pages 62–67 (2005)Cite this article

Abstract

Transmission of information using the spin of the electron as well as its charge requires a high degree of spin polarization at surfaces. However, at surfaces this degree of polarization can be quenched by competing interactions. Using a combination of surface-sensitive X-ray and tunnelling probes, we show for the quasi-two-dimensional bilayer manganites that only the outermost Mn–O bilayer is affected: it is a 1-nm-thick insulator that exhibits no long-range ferromagnetic order, whereas the next bilayer displays the full spin polarization of the bulk. Such an abrupt localization of the surface effects is due to the two-dimensional nature of the layered manganite, and the loss of ferromagnetism is attributed to weakened double exchange in the reconstructed surface bilayer and a resultant antiferromagnetic phase. The creation of a well-defined surface insulator atop a fully spin-polarized bulk demonstrates the ability of two of the most demanding components of an ideal magnetic tunnel junction to self-assemble naturally.

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Figure 1: Structure of the naturally bilayered manganite La2–2xSr1+2xMn2O7.
Figure 2: Polarization-dependent scattering and absorption data at the Mn L3 edge.
Figure 3: Magnetic profile determination and temperature dependence of the bulk-like sub-surface bilayer.
Figure 4: The log current–voltage characteristics of numerous high-resistance Au point-contacts (PT) taken at 4.2 K on a crystal x = 0.36, plotted together with representative STS data taken well above TC.
Figure 5: Field-induced metal–insulator transition for a layered manganite with x = 0.48.

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Acknowledgements

The research, including the use of the Advanced Photon Source, was supported by the US Department of Energy (DOE), Basic Energy Sciences, under contract W-31-109-ENG-38.

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Authors and Affiliations

  1. Advanced Photon Source, Argonne National Laboratory, Argonne, 60439, Illinois, USA

    J. W. Freeland & J. Kavich

  2. Materials Science Division, Argonne National Laboratory, Argonne, 60439, Illinois, USA

    K. E. Gray, L. Ozyuzer, P. Berghuis, Elvira Badica, H. Zheng & J. F. Mitchell

  3. Department of Phyisics, Izmir Institute of Technology, Izmir, TR-35437, Turkey

    L. Ozyuzer

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Correspondence to J. W. Freeland.

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Freeland, J., Gray, K., Ozyuzer, L. et al. Full bulk spin polarization and intrinsic tunnel barriers at the surface of layered manganites. Nature Mater 4, 62–67 (2005). https://doi.org/10.1038/nmat1280

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