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The quantum spin-valve in cobalt atomic point contacts

Nature Materials volume 4, pages 832–837 (2005)Cite this article

Abstract

Magnetic materials reduced to a single atom show unexpected magnetic properties that interact with the spin states of the transmitting electrons and modify the nature of the quantized conductance. This integration of quantized conductance and spin-dependent transport across a magnetic atom gives rise to a multichannel system across which the transmission of electron waves can be regulated by a domain wall acting as a ‘valve’ —a quantum spin-valve. Here we measure complete magnetoresistance loops across magnetic quantum point contacts as small as a single atom, using cobalt. ‘Discrete’ or quantum magnetoresistance loops are observed owing to the varying transmission probability from the available discrete conductance channels. A remarkable feature of these quantum contacts is the discovery of a rapid oscillatory decay in magnetoresistance with increasing contact size. The results provide an evolutionary trace of spin-dependent transport from a single atom to larger ensembles.

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Figure 1: Electrical properties of cobalt quantum point contacts of various sizes, with contacts in the spin-split state formed in the presence of a constant magnetic field of approximately 600 Oe.
Figure 2: Low-magnification scanning electron microscope (Hitachi, model S-4000) image of the microfabricated electrodes between which a cobalt point contact of 0.5Go conductance was electrodeposited.
Figure 3: Quantum magnetoresistance loops showing the stepwise change in resistance with applied magnetic field in cobalt point contacts of various sizes along with an illustration of discrete conductance channels due to the transverse confinement of electron waves.
Figure 4: The oscillatory nature of magnetoresistance as a function of quantized conductance in the high-field (ferromagnetically aligned) state.

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Acknowledgements

The work was supported by NSF-DMR-FRG-03-05242. The authors thank D. Ateya for help in microfabrication of the templates and acknowledge P. Bush, South Campus Instrumentation Center, for help with scanning electron microscopy of the contacts. Microfabrication was performed, in part, at the Cornell Nanofabrication Facility, which is supported by the NSF Grant ECS-9731293, Cornell University, and industrial affiliates. The authors thank L. Deresh and D. Lashmore for suggestions on electrochemistry, and L. Bennett for pointing to the history of point contact transistors.

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  1. Harsh Deep Chopra and Susan Z. Hua: These authors contributed equally to this work

Authors and Affiliations

  1. Thin Films and Nanosynthesis Laboratory, Materials Program, Mechanical and Aerospace Engineering Department, State University of New York, Buffalo, New York, 14260, USA

    Harsh Deep Chopra, Matthew R. Sullivan, Jason N. Armstrong & Susan Z. Hua

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  1. Harsh Deep Chopra
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Correspondence to Harsh Deep Chopra or Susan Z. Hua.

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Chopra, H., Sullivan, M., Armstrong, J. et al. The quantum spin-valve in cobalt atomic point contacts. Nature Mater 4, 832–837 (2005). https://doi.org/10.1038/nmat1510

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