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Exchange-coupled nanocomposite magnets by nanoparticle self-assembly

Nature volume 420, pages 395–398 (2002)Cite this article

Abstract

Exchange-spring magnets are nanocomposites that are composed of magnetically hard and soft phases that interact by magnetic exchange coupling1. Such systems are promising for advanced permanent magnetic applications, as they have a large energy product—the combination of permanent magnet field and magnetization—compared to traditional, single-phase materials1,2,3. Conventional techniques, including melt-spinning4,5,6, mechanical milling7,8,9 and sputtering10,11,12, have been explored to prepare exchange-spring magnets. However, the requirement that both the hard and soft phases are controlled at the nanometre scale, to ensure efficient exchange coupling, has posed significant preparation challenges. Here we report the fabrication of exchange-coupled nanocomposites using nanoparticle self-assembly. In this approach, both FePt and Fe3O4 particles are incorporated as nanometre-scale building blocks into binary assemblies. Subsequent annealing converts the assembly into FePt–Fe3Pt nanocomposites, where FePt is a magnetically hard phase and Fe3Pt a soft phase. An optimum exchange coupling, and therefore an optimum energy product, can be obtained by independently tuning the size and composition of the individual building blocks. We have produced exchange-coupled isotropic FePt–Fe3Pt nanocomposites with an energy product of 20.1 MG Oe, which exceeds the theoretical limit of 13 MG Oe for non-exchange-coupled isotropic FePt by over 50 per cent.

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Figure 1: TEM images showing binary nanoparticle assemblies.
Figure 2: Structural analyses of the FePt–Fe3Pt nanocomposite obtained from the annealed Fe3O4 (4 nm):Fe58Pt42 (4 nm) assembly.
Figure 3: Ms, Mr and Hc of the FePt–Fe3Pt nanocomposites from the annealed Fe3O4 (4 nm):Fe58Pt42 (4 nm) assemblies as a function of mass ratio of Fe3O4:FePt.
Figure 4: Typical hysteresis loops of two FePt-based nanocomposites.
Figure 5: Second-quadrant B–H curves for the annealed samples.

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References

  1. Kneller, E. F. & Hawig, R. The exchange-spring magnet: a new material principle for permanent magnets. IEEE Trans. Magn. 27, 3588–3600 (1991)

    Article  ADS  CAS  Google Scholar 

  2. Skomski, R. & Coey, J. M. D. Giant energy product in nanostructured two-phase magnets. Phys. Rev. B 48, 15812–15816 (1993)

    Article  ADS  CAS  Google Scholar 

  3. Schrefl, T., Kronmüller, H. & Fidler, J. Exchange hardening in nano-structured two-phase permanent magnets. J. Magn. Mag. Mater. 127, L273–L277 (1993)

    Article  ADS  CAS  Google Scholar 

  4. Coehoorn, R., De Mooij, D. B. & De Waard, C. Meltspun permanent magnet materials containing Fe3B as the main phase. J. Magn. Mag. Mater. 80, 101–104 (1989)

    Article  ADS  CAS  Google Scholar 

  5. Ping, D. H., Hono, K. & Hirosawa, S. Partitioning of Ga and Co atoms in a Fe3B/Nd2Fe14B nanocomposite magnet. J. Appl. Phys. 83, 7769–7775 (1998)

    Article  ADS  CAS  Google Scholar 

  6. Kobayashi, T., Yamasaki, M. & Hamano, M. Mössbauer study on intergranular phases in the bcc-Fe/NdFeB nanocomposite alloys. J. Appl. Phys. 87, 6579–6581 (2000)

    Article  ADS  CAS  Google Scholar 

  7. Gong, W., Hadjipanayis, G. C. & Krause, R. F. Mechanically alloyed nanocomposite magnets. J. Appl. Phys. 75, 6649–6651 (1994)

    Article  ADS  Google Scholar 

  8. McCormick, P. G. et al. Mechanically alloyed nanocomposite magnets. J. Appl. Phys. 83, 6256–6261 (1998)

    Article  ADS  CAS  Google Scholar 

  9. Zhang, J., Zhang, S.-Y., Zhang, H.-W., Shen, B.-G. & Li, B.-H. Structure and magnetic properties of SmxCo5/α-Fe (x = 0.65-1.3) prepared by mechanical milling and subsequent annealing. J. Appl. Phys. 89, 2857–2860 (2001)

    Article  ADS  CAS  Google Scholar 

  10. Fullerton, E. E., Jiang, J. S., Sowers, C. H., Pearson, J. E. & Bader, S. D. Structure and magnetic properties of exchange-spring Sm-Co/Co superlattices. Appl. Phys. Lett. 72, 380–382 (1997)

    Article  ADS  Google Scholar 

  11. Liu, J. P., Luo, C. P., Liu, Y. & Sellmyer, D. J. High energy products in rapidly annealed nanoscale Fe/Pt multilayers. Appl. Phys. Lett. 72, 483–485 (1998)

    Article  ADS  CAS  Google Scholar 

  12. Liu, J. P., Liu, Y., Skomski, R. & Sellmyer, D. J. Magnetic hardening in SmCox-Co multilayers and nanocomposites. J. Appl. Phys. 85, 4812–4814 (1999)

    Article  ADS  CAS  Google Scholar 

  13. 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  ADS  CAS  Google Scholar 

  14. Sun, S., Fullerton, E. E., Weller, D. & Murray, C. B. Compositionally controlled FePt nanoparticle materials. IEEE Trans. Magn. 37, 1239–1243 (2001)

    Article  ADS  CAS  Google Scholar 

  15. Sun, S. & Zeng, H. Size controlled synthesis of magnetite nanoparticles. J. Am. Chem. Soc. 124, 8204–8205 (2002)

    Article  CAS  Google Scholar 

  16. Kiely, C. J., Fink, J., Brust, M., Bethell, D. & Schiffrin, D. J. Spontaneous ordering of bimodal ensembles of nanoscopic gold clusters. Nature 396, 444–446 (1998)

    Article  ADS  CAS  Google Scholar 

  17. Weller, D. et al. High Ku materials approach to 100 Gbits/in2. IEEE Trans. Magn. 36, 10–15 (2000)

    Article  ADS  CAS  Google Scholar 

  18. Klemmer, T., Hoydick, D., Okumura, H., Zhang, B. & Soffa, W. A. Magnetic hardening and coercivity mechanisms in L10 ordered FePd ferromagnets. Scripta Met. 33, 1793–1805 (1995)

    Article  CAS  Google Scholar 

  19. Podgorny, M. Electronic structure of the ordered phases of Pt-Fe alloys. Phys. Rev. B 43, 13700–13718 (1991)

    Article  Google Scholar 

  20. Zeng, H. et al. Exchange-coupled FePt nanoparticle assembly. Appl. Phys. Lett. 80, 2583–2585 (2002)

    Article  ADS  CAS  Google Scholar 

  21. O'Handley, R. C. Modern Magnetic Materials 469–472 (John Wiley & Sons, New York, 2000)

    Google Scholar 

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Acknowledgements

This work is supported in part by the US Defense Advanced Research Program Agency (DARPA) through the Army Research Office (ARO). H. Z. and J. L. thank DARPA for support through Louisiana Tech University.

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Authors and Affiliations

  1. IBM T. J. Watson Research Center, Yorktown Heights, New York, 10598, USA

    Hao Zeng & Shouheng Sun

  2. Institute for Micromanufacturing, Louisiana Tech University, Ruston, Louisiana, 71272, USA

    Hao Zeng & J. P. Liu

  3. School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, 30332, USA

    Jing Li & Zhong L. Wang

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  1. Hao Zeng
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Correspondence to Shouheng Sun.

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Zeng, H., Li, J., Liu, J. et al. Exchange-coupled nanocomposite magnets by nanoparticle self-assembly. Nature 420, 395–398 (2002). https://doi.org/10.1038/nature01208

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