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:

Collective behaviour in two-dimensional cobalt nanoparticle assemblies observed by magnetic force microscopy

Nature Materials volume 3, pages 263–268 (2004)Cite this article

Abstract

The use of magnetic nanoparticles in the development of ultra-high-density recording media is the subject of intense research. Much of the attention of this research is devoted to the stability of magnetic moments, often neglecting the influence of dipolar interactions. Here, we explore the magnetic microstructure of different assemblies of monodisperse cobalt single-domain nanoparticles by magnetic force microscopy and magnetometric measurements. We observe that when the density of particles per unit area is higher than a determined threshold, the two-dimensional self-assemblies behave as a continuous ferromagnetic thin film. Correlated areas (similar to domains) of parallel magnetization roughly ten particles in diameter appear. As this magnetic percolation is mediated by dipolar interactions, the magnetic microstructure, its distribution and stability, is strongly dependent on the topological distribution of the dipoles. Thus, the magnetic structures of three-dimensional assemblies are magnetically soft, and an evolution of the magnetic microstructure is observed with consecutive scans of the microscope tip.

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

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

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

Figure 1: Topography and magnetic structure of a Co nanoparticle compact monolayer.
Figure 2: Topography and magnetic structure of a Co nanoparticle incomplete layer.
Figure 3: Topography and magnetic structure of a Co nanoparticle monolayer with different particle densities.
Figure 4: Topography and magnetic structure of Co nanoparticle islands.
Figure 5: Dependence of the local magnetization as a function of the particle density.
Figure 6: Magnetization measurements as a function of field orientation and temperature.
Figure 7: Topography and magnetic structure of a Co nanoparticle multilayer.

Similar content being viewed by others

References

  1. Seul, M. & Andelman, D. Domain shapes and patterns: the phenomenology of modulated phases. Science 267, 476–483 (1995).

    Article  CAS  Google Scholar 

  2. Vidal Russell, E. & Israeloff, N.E. Direct observation of molecular cooperativity near the glass transition. Nature 408, 695–698 (2000).

    Article  Google Scholar 

  3. Young, A.P. Spin Glasses and Random Fields (World Scientific, Singapore, 1998).

    Google Scholar 

  4. Parisi, G. Complex systems: a physicist's viewpoint. Physica A 263, 557–564 (1999).

    Article  Google Scholar 

  5. Sun, S. & Murray, C.B. Synthesis of monodisperse cobalt nanocrystals and their assembly into magnetic superlattices (invited). J. Appl. Phys. 85, 4325–4390 (1999).

    Article  CAS  Google Scholar 

  6. Sun, S., Murray, C.B., Weller, D., Folks, L. & Moser, A. Monodisperse FePt nanoparticles and ferromagnetic FePt nanocrystal superlattices. Science 287, 1989–1992 (2000).

    Article  CAS  Google Scholar 

  7. Weiss, J. Simulation of quasi-two-dimensional dipolar systems. J. Phys. Condens. Matter 15, S1471–S1495 (2003).

    Article  Google Scholar 

  8. Puntes, V.F., Alivisatos, A.P. & Krishnan, K. Synthesis, self-assembly, and magnetic behavior of a two-dimensional superlattice of single-crystal ε-Co nanoparticles. Appl. Phys. Lett. 78, 2187–2199 (2001).

    Article  CAS  Google Scholar 

  9. Porthun, S., Abelmann, L. & Lodder, C. Magnetic force microscopy of thin film media for high-density magnetic recording. J. Magn. Magn. Mater. 182, 238–273 (1998).

    Article  CAS  Google Scholar 

  10. Folks, L. & Woodward, R.C. The use of MFM for investigating domain structures in modern permanent magnet materials. J. Magn. Magn. Mater. 190, 28–41 (1998).

    Article  CAS  Google Scholar 

  11. Babcock, K.L., Elings, V.B., Shi, J., Awschalom, D.D. & Dugas, M. Field-dependence of microscopic probes in magnetic force microscopy. Appl. Phys. Lett. 69, 705–707 (1996).

    Article  CAS  Google Scholar 

  12. Vellekoop, S.J.L., Abelmann, L., Porthun, S., Lodder, J.C. & Miles, J.J. Calculation of playback signals from MFM images using transfer functions. J. Magn. Magn. Mater. 193, 474–478 (1999).

    Article  CAS  Google Scholar 

  13. Kleiber, M. et al. Magnetization switching of submicrometer Co dots induced by a magnetic force microscope tip. Phys. Rev. B 58, 5563–5567 (1998).

    Article  CAS  Google Scholar 

  14. Gider, S. et al. Imaging and magnetometry of switching in nanometer-scale iron particles. Appl. Phys. Lett. 69, 3269–3271 (1996).

    Article  CAS  Google Scholar 

  15. Proksch, R.B. et al. MFM of the submicron magnetic assembly in magnetotactic bacterium. Appl. Phys. Lett. 66, 2582–2584 (1995).

    Article  CAS  Google Scholar 

  16. Sun, S. et al. Polymer mediated self-assembly of magnetic nanoparticles. J. Am. Chem. Soc. 124, 2884–2885 (2002).

    Article  CAS  Google Scholar 

  17. Rasa, M., Kuipers, B.W.M. & Philipse, A.P. Atomic force microscopy and magnetic force microscopy study of model colloids. J. Colloid Interface Sci. 250, 303–315 (2002).

    Article  CAS  Google Scholar 

  18. Majetich, S.A. & Jin, Y. Magnetization directions of individual nanoparticles. Science 284, 470–473 (1999).

    Article  CAS  Google Scholar 

  19. Yamasaki, A., Wulfhekel, W., Hertel, R. & Kirschner, J. Direct observation of the single-domain limit of Fe nanomagnets by spin-polarized scanning tunneling spectroscopy. Phys. Rev. Lett. 91, 127201 (2003).

    Article  CAS  Google Scholar 

  20. Kubetzka, A., Bode, M., Pietzsch, O. & Wiesendanger, R. Spin-polarized scanning tunneliung microscopy with antiferromagnetic probe tips. Phys. Rev. Lett. 88, 057201 (2002).

    Article  CAS  Google Scholar 

  21. Respaud, M. et al. Surface effects on the magnetic properties of ultrafine cobalt particles. Phys. Rev. B 57, 2925–2935 (1998).

    Article  CAS  Google Scholar 

  22. Binns, C., Maher, M.J., Pankhurst, Q.A., Kechrakos, D. & Trohidou, K.N. Magnetic behavior of nanostructured films assembled from preformed Fe clusters embedded in Ag. Phys. Rev. B 66, 184413 (2002).

    Article  Google Scholar 

  23. Padovani, S., Chado, I., Scheurer, F. & Bucher, J.P. Transition from zero-dimensional superparamagnetism to two-dimensional ferromagnetism of Co clusters on Au. Phys. Rev. B 59, 11887–11891 (1999).

    Article  CAS  Google Scholar 

  24. Russier, V., Petit, C. & Pileni, M.P. Hysteresis curve of magnetic nanocrystals monolayers: influence of the structure. J. Appl. Phys. 93, 10001–10010 (2003).

    Article  CAS  Google Scholar 

  25. Franco-Puntes, V., Batlle, X. & Labarta, A. Evidence of domain wall scattering in thin films of granular CoFe-AgCu. European Phys. J. B 17, 43–51 (2000).

    Article  Google Scholar 

  26. Hu, J., Xiao, X.-D., Ogletree, D.F. & Salmeron, M. Imaging the condensation and evaporation of molecularly thin films of water with nanometer resolution. Science 269, 267–269 (1995).

    Article  Google Scholar 

  27. Fredkin, D.R. & Koehler, T.R. Micromagnetic modeling of permalloy particles: thickness effects. IEEE Trans. Magn. 27, 4763–4765 (1991).

    Article  Google Scholar 

  28. Xiao, J.Q., Chien, C.L. & Gavrin, A. Observation of perpendicular anisotropy in granular magnetic solids. J. Appl. Phys. 79, 5309–5311 (1997).

    Article  Google Scholar 

  29. Puntes, V.F. & Krishnan, K. Synthesis, structural order and magnetic behavior of self-assembled epsilon-Co nanocrystal arrays. IEEE Trans. Magn. 37, 2210–2212 (2001).

    Article  CAS  Google Scholar 

  30. Lederman, M., Fredkin, D.R., O'Barr, R., Schultz, S. & Ozaki, M. Measurement of thermal switching of the magnetization of single domain particles (invited). J. Appl. Phys. 75, 6217–6222 (1994).

    Article  CAS  Google Scholar 

  31. Peng, D.L., Sumiyama, K., Hihara, T. & Yamamuro, S. Enhancement of magnetic coercivity and macroscopic quantum tunneling in monodispersed Co/CoO cluster assemblies. Appl. Phys. Lett. 75, 3856–3858 (1999).

    Article  CAS  Google Scholar 

  32. Dinega, D.P. & Bawendi, M.G. A Solution-phase chemical approach to a new crystal structure of cobalt. Angew. Chem. Intl Edn Engl. 38, 1788–1791 (1999).

    Article  CAS  Google Scholar 

  33. Skumryev, V. et al. Beating the superparamagnetic limit with exchange bias. Nature 423, 850–853 (2003).

    Article  CAS  Google Scholar 

  34. Gambardella, P. et al. Giant magnetic anisotropy of single cobalt atoms and nanoparticles. Science 300, 1130–1132 (2003).

    Article  CAS  Google Scholar 

  35. Puntes, V.F., Krishnan, K. & Alivisatos, P. Nanocrystals size and shape control: the case of Co. Science 291, 2115–2117 (2001).

    Article  CAS  Google Scholar 

  36. Puntes, V.F., Zanchet, D., Erdonmez, C. & Alivisatos, A.P. Synthesis of hcp-Co nanodisks. J. Am. Chem. Soc. 124, 12874–12880 (2002).

    Article  CAS  Google Scholar 

  37. Colvin, V.L., Goldstein, A.N. & Alivisatos, A.P. Semiconductor nanocrystals covalently bound to metal surfaces using self assembled monolayers. J. Am. Chem. Soc. 114, 5221–5230 (1992).

    Article  CAS  Google Scholar 

  38. Ebenstein, Y., Nahum, E. & Banin, U. Tapping mode atomic force microscopy for nanoparticle sizing: Tip-sample interaction effects. Nano Lett. 2, 945–950 (2002).

    Article  CAS  Google Scholar 

  39. Kebe, Th. & Carl, A. Calibration of magnetic force microscopy tips by using nanoscale current-carrying parallel wires. J. App. Phys. 95, 775–792 (2004).

    Article  CAS  Google Scholar 

  40. Graps, A. An introduction to wavelets. IEEE Comput. Sci. Eng. 2, 50–61 (1995).

    Article  Google Scholar 

Download references

Acknowledgements

We thank the technical help and scientific discussion with Peter Nilson from Digital Instruments and Antonio Turiel from the University of Barcelona. Funding came from SEUID MAT2003-01124, DURSI 2001SGR00066, NIH 1 R01 RR-14891-01 and DE-AC03-76SF00098.

Author information

Authors and Affiliations

  1. Physics Department, University of Barcelona, Barcelona, 08028, Spain

    Victor F. Puntes & Neus G. Bastus

  2. Department of Molecular and Cell Biology, University of California, Berkeley, 94720, Berkeley, USA

    Pau Gorostiza

  3. College of Chemistry, University of California, Berkeley, 94720, Berkeley, USA

    Deborah M. Aruguete & A. Paul Alivisatos

Authors
  1. Victor F. Puntes
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Pau Gorostiza
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Deborah M. Aruguete
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Neus G. Bastus
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. A. Paul Alivisatos
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Victor F. Puntes.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Puntes, V., Gorostiza, P., Aruguete, D. et al. Collective behaviour in two-dimensional cobalt nanoparticle assemblies observed by magnetic force microscopy. Nature Mater 3, 263–268 (2004). https://doi.org/10.1038/nmat1094

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nmat1094

This article is cited by

Search

Advanced 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