Skip to main content
SpringerLink
Log in

Electromotive force and huge magnetoresistance in magnetic tunnel junctions

  • Letter
  • Published:

From Nature

View current issue Submit your manuscript

Abstract

The electromotive force (e.m.f.) predicted by Faraday’s law reflects the forces acting on the charge, –e, of an electron moving through a device or circuit, and is proportional to the time derivative of the magnetic field. This conventional e.m.f. is usually absent for stationary circuits and static magnetic fields. There are also forces that act on the spin of an electron; it has been recently predicted1,2 that, for circuits that are in part composed of ferromagnetic materials, there arises an e.m.f. of spin origin even for a static magnetic field. This e.m.f. can be attributed to a time-varying magnetization of the host material, such as the motion of magnetic domains in a static magnetic field, and reflects the conversion of magnetic to electrical energy. Here we show that such an e.m.f. can indeed be induced by a static magnetic field in magnetic tunnel junctions containing zinc-blende-structured MnAs quantum nanomagnets. The observed e.m.f. operates on a timescale of approximately 102–103 seconds and results from the conversion of the magnetic energy of the superparamagnetic MnAs nanomagnets into electrical energy when these magnets undergo magnetic quantum tunnelling. As a consequence, a huge magnetoresistance of up to 100,000 per cent is observed for certain bias voltages. Our results strongly support the contention that, in magnetic nanostructures, Faraday’s law of induction must be generalized to account for forces of purely spin origin. The huge magnetoresistance and e.m.f. may find potential applications in high sensitivity magnetic sensors, as well as in new active devices such as ‘spin batteries’.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Log in via an institution

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Figure 1: Device structure.
Figure 2: Transport characteristics of an MTJ.
Figure 3: Huge magnetoresistance.
Figure 4: Magnetic energy.

Similar content being viewed by others

References

  1. Barnes, S. E. & Maekawa, S. Generalization of Faraday’s law to include nonconservative spin forces. Phys. Rev. Lett. 98, 246601 (2007)

    Article  ADS  CAS  Google Scholar 

  2. Barnes, S. E. Spin motive forces, “measurements”, and spin-valves. J. Magn. Magn. Mater. 310, 2035–2037 (2007)

    Article  ADS  CAS  Google Scholar 

  3. Fulton, T. A. & Dolan, G. J. Observation of single-electron charging effects in small tunnel junctions. Phys. Rev. Lett. 59, 109–112 (1987)

    Article  ADS  CAS  Google Scholar 

  4. Sanvito, S. & Hill, A. N. Ground state of half-metallic zinc-blende MnAs. Phys. Rev. B 62, 15553–15560 (2000)

    Article  ADS  CAS  Google Scholar 

  5. Sato, K., Katayama–Yoshida, H. & Dederichs, P. H. High Curie temperature and nano-scale spinodal decomposition phase in dilute magnetic semiconductors. Jpn. J. Appl. Phys. 44, L948–L951 (2005)

    Article  CAS  Google Scholar 

  6. Moreno, M., Trampert, A., Jenichen, B., Daweritz, L. & Ploog, K. H. Correlation of structure and magnetism in GaAs with embedded Mn(Ga)As magnetic nanoclusters. J. Appl. Phys. 92, 4672–4677 (2002)

    Article  ADS  CAS  Google Scholar 

  7. Yokoyama, M., Yamaguchi, H., Ogawa, T. & Tanaka, M. Zinc-blende-type MnAs nanoclusters embedded in GaAs. J. Appl. Phys. 97, 10D317 (2005)

    Article  Google Scholar 

  8. Kwiatkowski, A. et al. Structure and magnetism of MnAs nanocrystals embedded in GaAs as a function of post-growth annealing temperature. J. Appl. Phys. 101, 113912 (2007)

    Article  ADS  Google Scholar 

  9. Binasch, G., Grünberg, P., Saurenbach, F. & Zinn, W. Enhanced magnetoresistance in layered magnetic structures with antiferromagnetic interlayer exchange. Phys. Rev. B 39, 4828–4830 (1989)

    Article  ADS  CAS  Google Scholar 

  10. Baibich, M. N. et al. Giant magnetoresistance of (001)Fe/(001)Cr magnetic superlattices. Phys. Rev. Lett. 61, 2472–2475 (1988)

    Article  ADS  CAS  Google Scholar 

  11. Moodera, J. S., Kinder, L. R., Wong, T. M. & Meservey, R. Large magnetoresistance at room temperature in ferromagnetic thin film tunnel junctions. Phys. Rev. Lett. 74, 3273–3276 (1995)

    Article  ADS  CAS  Google Scholar 

  12. Miyazaki, T. & Tezuka, N. Giant magnetic tunnelling effect in Fe/Al2O3/Fe junction. J. Magn. Magn. Mater. 139, L231–L234 (1995)

    Article  ADS  CAS  Google Scholar 

  13. Parkin, S. S. P. Giant tunnelling magnetoresistance at room temperature with MgO (100) tunnel barriers. Nature Mater. 3, 862–867 (2004)

    Article  ADS  CAS  Google Scholar 

  14. Yuasa, S., Nagahama, T., Fukushima, A., Suzuki, Y. & Ando, K. Giant room-temperature magnetoresistance in single-crystal Fe/MgO/Fe magnetic tunnel junctions. Nature Mater. 3, 868–871 (2004)

    Article  ADS  CAS  Google Scholar 

  15. Jin, S. et al. Thousandfold change in resistivity in magnetoresistive La-Ca-Mn-O films. Science 264, 413–415 (1994)

    Article  ADS  CAS  Google Scholar 

  16. Tokura, Y. (ed.) Advances in Condensed Matter Science Vol. 2, Colossal Magnetoresistance Oxides (Gordon & Breach, 2000)

    Google Scholar 

  17. Barnes, S. E., Ieda, J. & Maekawa, S. Magnetic memory and current amplification devices using moving domain walls. Appl. Phys. Lett. 89, 122507 (2006)

    Article  ADS  Google Scholar 

  18. Barnes, S. E. & Maekawa, S. Currents induced by domain wall motion in thin ferromagnetic wires. Preprint at 〈http://arxiv.org/abs/cond-mat/0410021v1〉 (2004)

  19. Barbara, B. et al. Mesoscopic quantum tunnelling of magnetization. J. Magn. Magn. Mater. 140–144, 1825–1828 (2002)

    Google Scholar 

  20. Tanaka, M. et al. Epitaxial orientation and magnetic properties of MnAs thin films grown on (001) GaAs: Template effects. Appl. Phys. Lett. 65, 1964–1966 (1994)

    Article  ADS  CAS  Google Scholar 

  21. Tanaka, M. Ferromagnet (MnAs)/III–V semiconductor hybrid structures. Semicond. Sci. Technol. 17, 327–341 (2002)

    Article  ADS  CAS  Google Scholar 

Download references

Acknowledgements

This work was partly supported by Grant-in-Aids for Scientific Research No. 18106007, No. 19048018 and No. 20686002, the Special Coordination Programs for Promoting Science and Technology, and R&D for Next-Generation Information Technology by MEXT, PRESTO of JST, and EPSRC (UK). We thank B.-H. Yu for his help in the transport measurements. P.N.H. acknowledges a JSPS Research Fellowship for Young Scientists and the Global COE Program (CO4).

Author Contributions P.N.H. designed the experiment, fabricated the samples, collected most of data and performed analysis of data; S.O. set up measurement apparatuses and gave experimental advice; M.T. managed and planned the research and supervised the experiment; and S.E.B. and S.M. developed the theoretical explanation of the experiment. All authors discussed the results and commented on the manuscript.

Author information

Authors and Affiliations

  1. Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan,

    Pham Nam Hai, Shinobu Ohya & Masaaki Tanaka

  2. Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi-shi 332-0012, Japan ,

    Shinobu Ohya & Masaaki Tanaka

  3. Physics Department, University of Miami, Coral Gables, Florida 33124, USA,

    Stewart E. Barnes

  4. TCM, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK

    Stewart E. Barnes

  5. Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

    Sadamichi Maekawa

  6. CREST, Japan Science and Technology Agency, Tokyo 100-0075, Japan

    Sadamichi Maekawa

Authors
  1. Pham Nam Hai
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Shinobu Ohya
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Masaaki Tanaka
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Stewart E. Barnes
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Sadamichi Maekawa
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Masaaki Tanaka.

Supplementary information

Supplementary Information

This file contains Supplementary Notes, Supplementary Figures S1-S5 with Legends and Supplementary References (PDF 835 kb)

PowerPoint slides

Rights and permissions

Reprints and permissions

About this article

Cite this article

Hai, P., Ohya, S., Tanaka, M. et al. Electromotive force and huge magnetoresistance in magnetic tunnel junctions. Nature 458, 489–492 (2009). https://doi.org/10.1038/nature07879

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nature07879

  • Springer Nature Limited

This article is cited by

Search

Navigation