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Segregation phenomena in Nd–Fe–B nanoparticles

  • F. Schmidt
  • D. Pohl
  • L. Schultz
  • B. Rellinghaus
Research Paper

Abstract

We report on the phase stability and phase formation of Nd–Fe–B nanoparticles from the gas phase in the size range from 10 to 25 nm. Particular attention is paid to the question, if the intermetallic \(\hbox {Nd}_{2}\hbox {Fe}_{14}\hbox {B}\) phase also forms in free particles with a few nanometers in size that grow without contact to any solid or liquid matrix in a low pressure Ar atmosphere. The paper also addresses the possible influence of segregation phenomena that go along with the phase formation and the effect of (rapid) thermal annealing on the structure and phase stability of the particles. Aberration-corrected transmission electron microscopy in combination with spectroscopic methods was used to determine the local atomic structure and the chemical composition of the particles. Unheated particles are found to be mainly amorphous, while the rapidly optically annealed particles are crystalline. In both cases, we observe an enrichment of Nd in the shell of the particles and a Fe enrichment in the core. This segregation of Nd toward the particles' surface is more pronounced in heated particles, which form a clear core-shell structure with a Fe core surrounded by a \(\hbox {Nd}_{2}\hbox {O}_{3}\) shell. This finding is attributed to the comparably small surface energy and the higher affinity of Nd to oxygen as compared to Fe. A simple model is introduced and used in order to estimate these surface energies. These estimations support the experimentally observed segregation phenomena. It is further found that B prefers the vicinity of Fe over that of Nd atoms, which as a consequence leads to a B enrichment in the Fe-rich parts of the particles. Magnetic measurements show a soft magnetic behavior for both, unheated and heated Nd–Fe–B nanoparticles.

Keywords

Nd–Fe–B Nanoparticles Segregation Core-shell Transmission electron microscopy Nanomagnetism  Phase separation Janus 

References

  1. Akdogan NG, Hadjipanayis GC, Sellmyer DJ (2010) Novel \({\text{Nd}_{2}\text{Fe}_{14}\text{B}}\) nanoflakes and nanoparticles for the development of high energy nanocomposite magnets. Nanotechnology 21(29):295705Google Scholar
  2. Baletto F, Ferrando R (2005) Structural properties of nanoclusters: energetic, thermodynamic, and kinetic effects. Rev Mod Phys 77(1):371–423CrossRefGoogle Scholar
  3. Bieniek B, Pohl D, Schultz L, Rellinghaus B (2011) The effect of oxidation on the surface-near lattice relaxation in FeNi nanoparticles. J Nanopart Res 13(11):5935–5946CrossRefGoogle Scholar
  4. Bosman M, Keast VJ (2008) Optimizing EELS acquisition. Ultramicroscopy 108(9):837–846CrossRefGoogle Scholar
  5. Chen S-Y, Gloter A, Zobelli A, Wang L, Chen C-H, Colliex C (2009) Electron energy loss spectroscopy and ab initio investigation of iron oxide nanomaterials grown by a hydrothermal process. Phys Rev B 79(10):104103CrossRefGoogle Scholar
  6. Coey JMD (2001) Magnetic materials. J Alloys Compd 326(1–2):2–6CrossRefGoogle Scholar
  7. Coey JMD (2010) Magnetism and magnetic materials. Cambridge University Press, Cambridge ISBN 9780521816144CrossRefGoogle Scholar
  8. Colliex C, Manoubi T, Ortizu C (1991) Electron-energy-loss-spectroscopy near-edge fine-structures in the iron–oxygen system. Phys Rev B 44(20):11402–11411CrossRefGoogle Scholar
  9. Dempsey NM, Woodcock TG, Sepehri-Amin H, Zhang Y, Kennedy H, Givord D, Gutfleisch O (2013) High-coercivity Nd–Fe–B thick films without heavy rare earth additions. Acta Mater 61(13):4920–4927CrossRefGoogle Scholar
  10. Fu X, Han X, Du Z, Feng H, Li Y (2013) Microstructural investigation of Nd-rich phase in sintered Nd–Fe–B magnets through electron microscopy. J Rare Earths 31(8):765–771CrossRefGoogle Scholar
  11. Fu B-Q, Liu W, Li Z-L (2009) Calculation of the surface energy of hcp-metals with the empirical electron theory. Appl Surf Sci 255(23):9348–9357CrossRefGoogle Scholar
  12. Gubin SP, Koksharov YA, Khomutov GB, Yurkov GY (2005) Magnetic nanoparticles: preparation methods, structure and properties. Russ Chem Rev 74(6):489–520CrossRefGoogle Scholar
  13. Gutfleisch O (2000) Controlling the properties of high energy density permanent magnetic materials by different processing routes. J Phys D 33(17):R157–R172CrossRefGoogle Scholar
  14. Ibusuki T, Kojima S, Kitakami O, Shimada Y (2001) Magnetic anisotropy and behaviors of Fe nanoparticles. IEEE Trans Magn 37(4):2223–2225CrossRefGoogle Scholar
  15. Kang S, Shi S, Jia Z, Thomson GB, Nikles DE, Harrell JW, Li D, Poudyal N, Nandwana V, Liu JP (2007) Microstructures and magnetic alignment of \(\text{L}1_{0}\) FePt nanoparticles. J Appl Phys 101(9):09J113Google Scholar
  16. Krishnan G, Verheijen Ma, ten Brink GH, Palasantzas G, Kooi BJ (2013) Tuning structural motifs and alloying of bulk immiscible Mo–Cu bimetallic nanoparticles by gas-phase synthesis. Nanoscale 5(12):5375–5383CrossRefGoogle Scholar
  17. Lange N (1999) Handbook of chemistry, soil science, 15th edn. McGraw-Hill Professional, New YorkGoogle Scholar
  18. Lentzen M, Jahnen B, Jia CL, Thust A, Tillmann K, Urban K (2002) High-resolution imaging with an aberration-corrected transmission electron microscope. Ultramicroscopy 92(3–4):233–242CrossRefGoogle Scholar
  19. Liu WF, Suzuki S, Machida K (2007) Magnetic properties of Nd–Fe–B film magnets prepared by RF sputtering. J Magn Magn Mater 308(1):126–130CrossRefGoogle Scholar
  20. Mohn E (2012) Optische Kurzzeit-Wärmebehandlung von FePt-nanopartikeln im flug: Einfluss auf Struktur und Magnetismus. TU Dresden, IFW Dresden, PhD ThesisGoogle Scholar
  21. Mosendz O, Pisana S, Reiner JW, Stipe B, Weller D (2012) Ultra-high coercivity small-grain FePt media for thermally assisted recording. J Appl Phys 111(7):07B729CrossRefGoogle Scholar
  22. Perro A, Reculusa S, Ravaine S, Bourgeat-Lami E, Duguet E (2005) Design and synthesis of Janus micro- and nanoparticles. J Mater Chem 15(35–36):3745–3760CrossRefGoogle Scholar
  23. Pohl D, Surrey A, Schultz L, Rellinghaus B (2012) The impact of oxygen on the morphology of gas-phase prepared Au nanoparticles. Appl Phys Lett 101(26):263105CrossRefGoogle Scholar
  24. Pohl D, Wiesenhütter U, Mohn E, Schultz L, Rellinghaus B (2014) Near-surface strain in icosahedra of binary metallic alloys: segregational versus intrinsic effects. Nano Lett 14(4):1776–1784CrossRefGoogle Scholar
  25. Rellinghaus B, Stappert S, Wassermann EF, Sauer H, Spliethoff B (2001) The effect of oxidation on the structure of nickel nanoparticles. Phys J D 252:249–252Google Scholar
  26. Rellinghaus B, Mohn E, Schultz L, Gemming T, Acet M, Kowalik A, Kock BFF (2006) On the L10 ordering kinetics in Fe–Pt nanoparticles. IEEE Trans Magn 42(10):3048–3050CrossRefGoogle Scholar
  27. Roh K, Martin DC, Lahann J (2005) Biphasic Janus particles with nanoscale anisotropy. Nat Mater 4(10):759–763CrossRefGoogle Scholar
  28. Rong C, Li D, Nandwana V, Poudyal N, Ding Y, Wang ZL, Liu JP (2006) Size-dependent chemical and magnetic ordering in L10-FePt nanoparticles. Adv Mater 18(22):2984–2988CrossRefGoogle Scholar
  29. Schmidt F (2013) Optimierung des Lichtofens für das optische Heizen von Nanopartikeln im Flug und seine Anwendung bei der Herstellung von Nd–Fe–B-Partikeln. TU Dresden, IFW Dresden, Diploma ThesisGoogle Scholar
  30. Sepehri-Amin H, Ohkubo T, Shima T, Hono K (2012) Grain boundary and interface chemistry of an Nd–Fe–B-based sintered magnet. Acta Mater 60(3):819–830CrossRefGoogle Scholar
  31. Swaminathan V, Deheri PK, Bhame SD, Ramanujan RV (2013) Novel microwave assisted chemical synthesis of \(\text{Nd}_{2}\text{Fe}_{14}\text{B}\) hard magnetic nanoparticles. Nanoscale 5(7):2718–2725Google Scholar
  32. Weller D, Moser A, Folks L, Best ME, Toney MF, Schwickert M, Doerner MF (2000) High \(\text{K}_{{\rm u}}\) materials approach to \(100\,\text{Gbits/in}^2\). IEEE Trans Magn 36(1):10–15Google Scholar
  33. Woodcock TG, Khlopkov K, Walther a, Dempsey NM, Givord D, Schultz L, Gutfleisch O (2009) Interaction domains in high-performance NdFeB thick films. Scripta Mater 60(9):826–829CrossRefGoogle Scholar
  34. Woodcock TG, Zhang Y, Hrkac G, Ciuta G, Dempsey NM, Schrefl T, Givord D (2012) Understanding the microstructure and coercivity of high performance NdFeB-based magnets. Scripta Mater 67(6):536–541CrossRefGoogle Scholar
  35. Yu M, Liu Y, Liou SH, Sellmyer DJ (1998) Nanostructured NdFeB films processed by rapid thermal annealing. J Appl Phys 83(11):6611–6613CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2015

Authors and Affiliations

  • F. Schmidt
    • 1
    • 2
  • D. Pohl
    • 1
  • L. Schultz
    • 1
  • B. Rellinghaus
    • 1
  1. 1.IFW Dresden, Institute for Metallic MaterialsDresdenGermany
  2. 2.TU Dresden, Institute for Materials ScienceDresdenGermany

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