Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Unravelling the role of the interface for spin injection into organic semiconductors

Abstract

Organic materials are attractive for building spintronics devices owing to their expected long spin lifetimes. Moreover, the ability to control their properties by changing their composition and molecular structure makes them easier to tailor to given tasks than inorganic materials. However, most studies of candidate organic spintronics materials focus on their bulk spin transport characteristics. Here we investigate the equally important process of spin injection and how it is influenced by interface coupling in the prototype organic semiconductor, Alq3. We fabricate nanometre-scale (La,Sr)MnO3/Alq3/Co magnetic tunnel junctions that exhibit a magnetoresistive response of up to 300%. Furthermore, we develop a spin transport model that describes the role of interfacial spin-dependent metal/molecule hybridization on the effective polarization allowing enhancement and even sign reversal of injected spins. We expect such insights to lead towards the molecular-level engineering of metal/organic interfaces to tailor spin injection and bring new electrical functionalities to spintronics devices.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Schematic drawing of the organic MTJ.
Figure 2: Control of the Alq3 thickness.
Figure 3: Magnetic-field dependence of the resistance.
Figure 4: Bias-voltage and temperature dependence of the magnetoresistance.
Figure 5: Model used for donor–acceptor-mediated transport.

Similar content being viewed by others

References

  1. Fert, A. Nobel lecture: Origin, development, and future of spintronics. Rev. Mod. Phys. 80, 1517–1530 (2008).

    Article  ADS  Google Scholar 

  2. Cuniberti, G., Richter, K. & Fagas, G. (eds) in Introducing Molecular Electronics Vol. 680 (Springer, 2005).

  3. Dediu, V., Hueso, L., Bergenti, I. & Taliani, C. Spin routes in organic semiconductors. Nature Mater. 8, 707–716 (2009).

    Article  ADS  Google Scholar 

  4. Sanvito, S. & Rocha, A. R. Molecular spintronics: The art of driving spin through molecules. J. Comput. Theor. Nanosci. 3, 624–642 (2006).

    Article  Google Scholar 

  5. Drew, A. J. et al. Direct measurement of the electronic spin diffusion length in a fully functional organic spin value by low-energy muon spin rotation. Nature Mater. 8, 109–114 (2009).

    Article  ADS  Google Scholar 

  6. Cinchetti, M. et al. Determination of spin injection and transport in a ferromagnet/organic semiconductor heterojunction by two-photon photoemission. Nature Mater. 8, 115–119 (2009).

    Article  ADS  Google Scholar 

  7. Dediu, V., Murgia, M., Matacotta, F. C., Taliani, C. & Barbanera, S. Room temperature spin polarized injection in organic semiconductor. Solid State Commun. 122, 181–184 (2002).

    ADS  Google Scholar 

  8. Xiong, Z. H., Wu, D. & Vardeny, Z. V. Giant magnetoresistance in organic spin-valves. Nature 427, 821–824 (2004).

    Article  ADS  Google Scholar 

  9. Majumdar, S., Majumdar, H. S., Laiho, R. & Osterbacka, R. Comparing small molecules and polymer for future organic spin-valves. J. Alloys Compounds 423, 169–171 (2006).

    Article  Google Scholar 

  10. Wang, F. J., Yang, C. G., Vardeny, Z. V. & Li, X. Spin response in organic spin valves based on La2/3Sr1/3MnO3 electrodes. Phys. Rev. B 75, 245324 (2007).

    Article  ADS  Google Scholar 

  11. Xu, W. et al. Tunneling magnetoresistance observed in La2/3Sr1/3MnO3/organic molecule/Co junctions. Appl. Phys. Lett. 90, 072506 (2007).

    Article  ADS  Google Scholar 

  12. Hueso, L. E., Bergenti, I., Riminucci, A., Zhan, Y. Q. & Dediu, V. Multipurpose magnetic organic hybrid devices. Adv. Mater. 19, 2639–2642 (2007).

    Article  Google Scholar 

  13. Dediu, V. et al. Room-temperature spintronic effects in Alq3-based hybrid devices. Phys. Rev. B 78, 115203 (2008).

    Article  ADS  Google Scholar 

  14. Vinzelberg, H. et al. Low temperature tunneling magnetoresistance on (La,Sr)MnO3/Co junctions with organic spacer layers. J. Appl. Phys. 103, 093720 (2008).

    Article  ADS  Google Scholar 

  15. Santos, T. S. et al. Room-temperature tunnel magnetoresistance and spin-polarized tunneling through an organic semiconductor barrier. Phys. Rev. Lett. 98, 016601 (2007).

    Article  ADS  Google Scholar 

  16. Why going organic is good Nature Mater. 8, 691 (2009). 10.1038/nmat2517

  17. Sakaguchi, H. et al. Determination of performance on tunnel conduction through molecular wire using a conductive atomic force microscope. Appl. Phys. Lett. 79, 3708–3710 (2001).

    Article  ADS  Google Scholar 

  18. Matsumoto, R. et al. Oscillation of giant tunneling magnetoresistance with respect to tunneling barrier thickness in fully epitaxial Fe/MgO/Fe magnetic tunnel junctions. Appl. Phys. Lett. 90, 252506 (2007).

    Article  ADS  Google Scholar 

  19. Zhan, Y. Q. et al. Alignment of energy levels at the Alq3/La0.7Sr0.3MnO3 interface for organic spintronic devices. Phys. Rev. B 76, 045406 (2007).

    Article  ADS  Google Scholar 

  20. Akkerman, H. B. et al. Electron tunneling through alkanedithiol self-assembled monolayers in large-area molecular junctions. Proc. Natl Acad. Sci. USA 104, 11161–11166 (2007).

    Article  ADS  Google Scholar 

  21. Vàzquez, H., Flores, F. & Kahn, A. Induced density of states model for weakly interacting organic semiconductor interfaces. Org. Electron. 8, 241–248 (2007).

    Article  Google Scholar 

  22. Bratkovsky, A. M. Assisted tunneling in ferromagnetic junctions and half-metallic oxides. Appl. Phys. Lett. 72, 2334–2336 (1998).

    Article  ADS  Google Scholar 

  23. Bernand-Mantel, A. et al. Evidence for spin injection in a single metallic nanoparticle: A step towards nanospintronics. Appl. Phys. Lett. 89, 062502 (2006).

    Article  ADS  Google Scholar 

  24. Bowen, M. et al. Observation of Fowler–Nordheim hole regime across an electron tunnel junction due to total symmetry filtering. Phys. Rev. B 73, 140408(R) (2006).

    Article  ADS  Google Scholar 

  25. Mattana, R. et al. Chemical profile and magnetoresistance of Ga1−xMnxAs/GaAs/AlAs/GaAs/Ga1−xMnxAs tunnel junctions. Phys. Rev. B 71, 075206 (2005).

    Article  ADS  Google Scholar 

  26. Wang, W. & Richter, C. A. Spin-polarized inelastic electron tunneling spectroscopy of a molecular magnetic tunnel junction. Appl. Phys. Lett. 89, 153105 (2006).

    Article  ADS  Google Scholar 

  27. Tautz, F. S. et al. Strong electron–phonon coupling at a metal/organic interface: PTCDA/Ag(111). Phys. Rev. B 65, 125405 (2002).

    Article  ADS  Google Scholar 

  28. DeTeresa, J. M. et al. Role of the metal–oxide interface in determining the spin polarization of magnetic tunnel junction. Science 286, 507–509 (1999).

    Article  Google Scholar 

  29. Meservey, R. & Tedrow, P. M. Spin-polarized electron-tunneling. Phys. Rep. 238, 173–243 (1994).

    Article  ADS  Google Scholar 

  30. Velev, J. P., Dowben, P. A., Tsymbal, E. Y., Jenkins, S. J. & Caruso, A. N. Interface effects in spin-polarized metal/insulator layered structures. Surf. Sci. Rep. 63, 400–425 (2008).

    ADS  Google Scholar 

  31. Caruso, A. N., Schulz, D. L. & Dowben, P. A. Metal hybridization and electronic structure of tris(8-hydroxyquinolato) aluminum (Alq(3)). Chem. Phys. Lett. 413, 321–325 (2005).

    Article  ADS  Google Scholar 

  32. Baldo, M. A. & Forrest, S. R. Interface-limited injection in amorphous organic semiconductors. Phys. Rev. B 64, 085201 (2001).

    Article  ADS  Google Scholar 

  33. Bässler, H. Charge transport in disordered organic photoconductors. Phys. Status Solidi B 175, 15–56 (1993).

    Article  ADS  Google Scholar 

  34. Nitzan, A. & Ratner, M. Electron transport in molecular wire junctions. Science 300, 1384–1389 (2003).

    Article  ADS  Google Scholar 

  35. Mujica, V., Kemp, M. & Ratner, M. Electron conduction in molecular wires I A scattering formalism. J. Chem. Phys. 101, 6849–6855 (1994).

    Article  ADS  Google Scholar 

  36. Vàzquez, H. et al. Dipole formation at metal/PTCDA interfaces: Role of the charge neutrality level. Europhys. Lett. 65, 802–808 (2004).

    Article  ADS  Google Scholar 

  37. Tsymbal, E. Y., Sokolov, A., Sabirianov, I. F. & Doudin, B. Resonant inversion of tunneling magnetoresistance. Phys. Rev. Lett. 90, 186602 (2003).

    Article  ADS  Google Scholar 

  38. Garcia, V. et al. Resonant tunneling magnetoresistance in MnAs/III–V/MnAs junctions. Phys. Rev. B 72, 081303 (2005).

    Article  ADS  Google Scholar 

  39. Reily Rocha, A. & Sanvito, S. Resonant magnetoresistance in organic spin valves. J. Appl. Phys. 101, 09B102 (2007).

    Article  Google Scholar 

  40. Bouzehouane, K. et al. Nanolithography based on real-time electrically controlled indentation with an atomic force microscope for nanocontact elaboration. Nano Lett. 3, 1599–1602 (2003).

    Article  ADS  Google Scholar 

Download references

Acknowledgements

We thank C. Carretero and R. Guillemet for technical assistance. We also thank S. Tatay-Aguilar, A. Riminucci, M. Prezioso, A-A. Drillien and E. Girard for fruitful discussions. We acknowledge the financial support from EU-FP6-STRP under Grant No. 033370 OFSPIN, French ANR-PNANO under grant SPINORGA and ALICANTE, RTRA Triangle de la Physique and C’Nano Ile de France.

Author information

Authors and Affiliations

Authors

Contributions

C.B., R.M. and P.S. carried out the project, including experimental work, data analysis, model conception and development and writing of the paper. P.G., L.H., I.B. and V.D. grew, characterized and provided the LSMO/Alq3 bilayers. K.B., S.F. and C.D. contributed to the nanolithography and final electrode growth for the samples. K.B., F.P. and A.F. participated in general discussions and writing of the paper.

Corresponding authors

Correspondence to Pierre Seneor or Richard Mattana.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Barraud, C., Seneor, P., Mattana, R. et al. Unravelling the role of the interface for spin injection into organic semiconductors. Nature Phys 6, 615–620 (2010). https://doi.org/10.1038/nphys1688

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nphys1688

This article is cited by

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing