Nanocrystallinity and magnetic property enhancement in melt-spun iron-rare earth-base hard magnetic alloys

  • H. A. Davies
  • A. Manaf
  • P. Z. Zhang
Materials Design


Refinement of the grain size below ~35 nm mean diameter in melt-spun FeNdB-base alloys leads to en-hancement of remanent polarization,Jr, above the level predicted by the Stoner-Wohlfarth theory for an aggregate of independent, randomly oriented, and uniaxial magnetic particles. This article summarizes the results of the recent systematic research on this phenomenon, including the influence of alloy compo-sition and processing conditions on the crystallite size, degree of enhancement ofJr, and maximum en-ergy product(BH)max. It has been shown that the effect can also occur in ternary FeNdB alloys, without the addition of silicon or aluminum, which was originally thought necessary, providing the nanocrystal-lites are not magnetically decoupled by a paramagnetic second phase. Values of(BH)max above 160 kJ m-3 have been achieved. The relationship between grain size,Jr, intrinsic coercivity,JHc, and(BH)max are discussed in terms of magnetic exchange coupling, anisotropy, and other parameters. Recent exten-sion of this work to the enhancement of properties in Fe-Mischmetal-Boron-base alloys and to bonded magnets with a nanocrystalline structure is also described.


hard magnets iron-neodymium alloys magnetic materials nanocrystallinity 


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  1. 1.
    J.J. Croat, J.F. Herbst, R.W. Lee, and F.E. Pinkerton, High Energy Product Nd-Fe-B Permanent Magnets,Appl. Phvx. Lett., Vol 44, 1984, p 148CrossRefGoogle Scholar
  2. 2.
    J.J. Croat, J.F. Herbst, R.W. Lee, and F.E. Pinkerton, Pr-Fe and Nd-Fe-Based Materials: A New Class of High Performance Per- manent Magnets,J. Appl. Phys., Vol 55, 1984, p 2078CrossRefGoogle Scholar
  3. 3.
    R.W. Lee, E.G. Brewer, and N.A. Schafel, Processing of Nco- dymium-lron-Boron Melt Spun Ribbons to Fully Dense Mag- nets,IEEE Trans. Magn., Vol MAG-21, 1985, p 1958CrossRefGoogle Scholar
  4. 4.
    A. Tokunaga, Y. Nozawa. K. Iwasaki, S. Tanigawa, and H. Harada, Magnetic Properties of Isotropie and Anisotropie Nd-Fe- B Bonded Magnets, Rare Earth Permanent Magnets,Proc. EMRS Symposium, l.R. Harris, Ed., Amsterdam, North Holland, 1989, p 80Google Scholar
  5. 5.
    R. Bergeron, R.W. McCallum, K. Kanavan, and J.E. Keem, Euro- pean Patent Application No. 0-195219 ECD Devices Inc. June 2, 1986Google Scholar
  6. 6.
    G.B. Clemente, J.E. Keem, and J.P. Bradley, The Microstructural and Compositional Influence upon HIREM Behavior in Nd2Fe14B,J. Appl. Phys., Vol 64, 1988, p 5299CrossRefGoogle Scholar
  7. 7.
    F. Matsumoto, H. Sakamoto, M. Komiya, and M. Fujikura, Ef- fects of Silicon and Aluminium Additions on Magnetic Proper- ties of Rapidly Quenched Nd-Fe-B Permanent Magnets,J. Appl. Phys., Vol 63, 1988, p 3507CrossRefGoogle Scholar
  8. 8.
    G.C. Hadjipanayis and W. Gong, Magnetic Hysteresis in Melt- Spun Nd-Fe-Al-B-Si Alloys with High Remanence,J. Appl. Phys., Vol 64, 1988, p 5559CrossRefGoogle Scholar
  9. 9.
    H.A. Davies, K.J.A. Mawella, R.A. Buckley, G.E. Carr, A. Manaf, and A. Jha, Compositional and Process Effects on Struc- tures and Properties of Fe-Nd-B-Based Ribbons and Magnets Produced by the Melt Spinning Route,Proc. Conf. Concerted European Action on Magnetism, I.V. Mitchell, Ed., Elsevier Applied Science, London, 1989, p 543Google Scholar
  10. 10.
    K. Yajima, H. Nakamura, O. Kohmoto, and T. Yoneyama, Micro- structure of Rapidly Quenched Nd-Fe-Zr-B Magnets,J. Appl. Phys., Vol 64, 1988, p 5528CrossRefGoogle Scholar
  11. 11.
    R. Coehoorn, D.B. De Mooij, and C. Dewaard, Melt Spun Perma- nent Magnet Materials Containing Fe3B as the Main Phase,J. Magn. Magn. Mater., Vol 80, 1989, p 101CrossRefGoogle Scholar
  12. 12.
    A. Manaf, R.A. Buckley, H.A. Davies, and M. Leonowicz, En- hanced Magnetic Properties in Rapidly Solidified FeNdB Based Alloys,J. Magn. Magn. Mater, Vol 101, 1991, p 360CrossRefGoogle Scholar
  13. 13.
    A. Manaf, M. Leonowicz, H.A. Davies, and R.A. Buckley, Effect of Grain Size and Microstructure on Magnetic Properties of Rap- idly Solidified Fe82.4Nd13.1B4.5,J. Appl. Phvs., Vol 70, 1991, p. 6366CrossRefGoogle Scholar
  14. 14.
    S.J. Dobson, R.A. Buckley, and H.A. Davies, “Novel Mischmetal-Iron-Boron and Permanent Magnets Alloys by the Rapid Solidification Route,” Proc. 12th Int. Rare Earth and Their Applications, University of West Australia, Canberra, 1992, p 92Google Scholar
  15. 15.
    W.P. Sequeira, S.J. Dobson, R.A. Buckley, and H.A. Davies, Magnetic Properties of Nanocrystalline Melt Spun Iron-Didym- ium-Boron Alloys,Mater. Lett., Vol 15, 1993, p 376CrossRefGoogle Scholar
  16. 16.
    G.E. Carr, H.A. Davies, and R.A. Buckley, Crystallite Size Deter- minations for Melt Spun Fe-Nd-B Permanent Magnet Alloys,Mater. Sci. Eng., Vol 99, 1980, p 147CrossRefGoogle Scholar
  17. 17.
    E.C. Stoner and E.P. Wohlfarth, A Mechanism of Magnetic Hys- teresis in Heterogeneous Alloys,Philos. Trans. Soc, Vol A240, 1948,p 599CrossRefGoogle Scholar
  18. 18.
    A. Manaf, M. Leonowicz, H.A. Davies, and R.A. Buckley, Nanocrystalline Fe-Nd-B Type Permanent Magnet Materials with Enhanced Remanence,Mater. Lett., Vol 13, 1992, p 194CrossRefGoogle Scholar
  19. 19.
    A. Manaf, R.A. Buckley, and H.A. Davies, New Nanocrystalline High Remanence Fe-Nd-B Alloys by Rapid Solidification,J. Magn. Magn. Mater., Vol 12, 1993, in pressGoogle Scholar
  20. 20.
    H.A. Davies, A. Manaf, M. Leonowicz, P.Z. Zhang, S.J. Dobson. and R.A. Buckley, “Nanocrystalline Structures and Enhancement of Remanence and Energy Product in Melt Spun Iron-Rare Earth- Boron Alloys for Permanent Magnets,” Proc. 1st Int. Conf. Nanostructured Materials, Cancun, Mexico, Sept 1992, Nano- structured Materials, in pressGoogle Scholar
  21. 21.
    A. Manaf, M. Al-Khafaji, P.Z. Zhang, H.A. Davies, R.A. Buck- ley, and W.M. Rainforth, Microstructure Analysis of Nanocrys- talline Fe-Nd-B Ribbons with Enhanced Hard Magnetic Proper- ties, .J. Magn. Magn. Mater., Vol 12, 1993. in pressGoogle Scholar
  22. 22.
    A. Manaf, M. Leonowicz, R.A. Buckley, and H.A. Davies, “High Coercivity Fe-Nd-B Rapidly Solidified Alloys with Additions of Dy, Nb, and Si,” Proc. 7th Int. Symp. Magnetic Anisotropy and Coercivity in Rare Earth Transition Metal Alloys. University of West Australia, Canberra, 1992, p 115Google Scholar
  23. 23.
    J.D. Livingston. “Iron-Rare Earth Permanent Magnets,” 8th Int. Workshop on Rare Earth Magnets and Their Applications, K.J. Strnat, Ed., University of Dayton. May 1985. p423Google Scholar
  24. 24.
    J.E. Keem, G.B. Clemente, A.M. Kadin, and R.W. McCallum, “Magnetism of HIREM Magnets,” in Hard and Soft Magnetic Materials with Applications including Superconductivity. Proc. Conf. ASM Materials Week ’87, J.A. Salsgiver, Ed., American Society for Metals, 1987, p 27Google Scholar
  25. 25.
    H. Fukunaga and H. Inoue, Effect of Intergrain Exchange Interac- tion on Magnetic Properties in Isotropie NdFeB Magnets,Jpn. J. Appl. Phys., Vol 31, 1992, p 1347CrossRefGoogle Scholar
  26. 26.
    G. Herzer, Grain Size Dependence of Coercivity and Permeabil- ity in Nanocrystalline Ferromagnets,IEEE Trans. Magn., Vol 26, 1990,p 1397CrossRefGoogle Scholar
  27. 27.
    A. Manaf, P.Z. Zhang, I. Ahmad, H.A. Davies, and R.A. Buckley, “Magnetic Properties and Microstructural Characterisation ol Isotropie Nanocrystalline Fe-Nd-B Based Alloys,” paper pre- sented at INTERMAG ’93, Stockholm.IEEE Trans. Mag., in pressGoogle Scholar
  28. 28.
    P.Z. Zhang, A. Manaf. and H.A. Davies. to be publishedGoogle Scholar

Copyright information

© ASM International 1993

Authors and Affiliations

  • H. A. Davies
    • 1
  • A. Manaf
    • 1
  • P. Z. Zhang
    • 1
  1. 1.Department of Engineering MaterialsUniversity of SheffieldSheffieldUK

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