Co–CoO nanoparticles prepared by reactive gas-phase aggregation

  • J. A. González
  • J. P. Andrés
  • J. A. De Toro
  • P. Muñiz
  • T. Muñoz
  • O. Crisan
  • C. Binns
  • J. M. Riveiro
Research Paper

Abstract

The technique of gas-phase aggregation has been used to prepare partially oxidized Co nanoparticles films by allowing a controlled flow of oxygen gas into the aggregation zone. This method differs from those previously reported, that is, the passivation of a beam of preformed particles in a secondary chamber and the conventional (low Ar pressure) reactive sputtering of Co to produce Co–CoO composite films. Transmission electron microscopy shows that the mean size of the particles is about 6 nm. For sufficiently high oxygen pressures, the nanoparticles films become super-paramagnetic at room temperature. X-ray diffraction patterns display reflections corresponding to fcc Co and fcc CoO phases, with an increasing dominance of the latter upon increasing the oxygen pressure in the aggregation zone, which is consistent with the observed reduction in saturation magnetization. The cluster films assembled with particles grown under oxygen in the condensation zone exhibit exchange-bias fields (about 8 kOe at 20 K) systematically higher than those measured for Co–CoO core-shell nanoparticles prepared by oxidizing preformed particles in the deposition chamber, which we attribute, in the light of results from annealing experiments, to a higher ferromagnetic–antiferromagnetic (Co–CoO) interface density.

Keywords

Co nanoparticles Gas-phase aggregation Exchange-bias Core-shell particles Aerosols Nanocomposites 

References

  1. Binns C, Maher MJ (2002) Magnetic behaviour of thin films produced by depositing pre-formed Fe and Co nanoclusters. N J Phys 4:85. doi:10.1088/1367-2630/4/1/385 CrossRefGoogle Scholar
  2. Brems S, Temst K, Van Haesendonck C (2007) Origin of the training effect and asymmetry of the magnetization in polycrystalline exchange bias systems. Phys Rev Lett 99:067201. doi:10.1103/PhysRevLett.99.067201 CrossRefPubMedADSGoogle Scholar
  3. De Toro JA, Andrés JP, González JA et al (2006) Exchange bias and nanoparticle magnetic stability in Co–CoO composites. Phys Rev B 73:094449. doi:10.1103/PhysRevB.73.094449 CrossRefADSGoogle Scholar
  4. Gredig T, Krivorotov IN, Dan Dahlberg E (2002) Magnetization reversal in exchange biased Co/CoO probed with anisotropic magnetoresistance. J Appl Phys 91:7760–7762. doi:10.1063/1.1447181 CrossRefADSGoogle Scholar
  5. Haberland H, Mall M, Moseler M et al (1994) Filling of micron-sized contact holes with copper by energetic cluster-impact. J Vac Sci Technol A 12:2925–2930. doi:10.1116/1.578967 CrossRefADSGoogle Scholar
  6. Heim DE, Fontana RE, Tsang C et al (1994) Design and operation of spin-valve sensors. IEEE Trans Magn 30:316–321. doi:10.1109/20.312279 CrossRefADSGoogle Scholar
  7. Hihara T, Peng DL, Sumiyama K (2001) Effects of O-2 gas on the size and structure of Cr clusters formed by plasma-gas-condensation. Mater Trans 42:1480–1484. doi:10.2320/matertrans.42.1480 CrossRefGoogle Scholar
  8. Hong JI, Leo T, Smith DJ et al (2006) Enhancing exchange bias with diluted antiferromagnets. Phys Rev Lett 96:117204. doi:10.1103/PhysRevLett.96.117204 CrossRefPubMedADSGoogle Scholar
  9. Koch SA, Palasantzas G, Vystavel T et al (2005) Magnetic and structural properties of Co nanocluster thin films. Phys Rev B 71:085410. doi:10.1103/PhysRevB.71.085410 CrossRefADSGoogle Scholar
  10. Lin X, Hadjipanayis GC, Shah SI (1994) Magnetic and structural-properties of Co/CoO bilayers. J Appl Phys 75:6676–6678. doi:10.1063/1.356892 CrossRefADSGoogle Scholar
  11. Meiklejohn WH, Bean CP (1957) New magnetic anisotropy. Phys Rev 102:1413–1414. doi:10.1103/PhysRev.102.1413 CrossRefADSGoogle Scholar
  12. Morel R, Brenac A, Portemont C (2004) Exchange bias and coercivity in oxygen-exposed cobalt clusters. J Appl Phys 95:3757–3760. doi:10.1063/1.1649818 CrossRefADSGoogle Scholar
  13. Nogués J, Sort J, Langlais V et al (2005) Exchange bias in nanostructures. Phys Rep 422:65–117ADSGoogle Scholar
  14. Normile PS, De Toro JA, Andrés JP et al (2006) Improvement of magnetic particle stability upon annealing in an exchange-biased nanogranular system. J Appl Phys 100:064312. doi:10.1063/1.2338134 CrossRefADSGoogle Scholar
  15. Normile PS, De Toro JA, Muñoz T et al (2007) Influence of spacer layer morphology on the exchange-bias properties of reactively sputtered Co/Ag multilayers. Phys Rev B 76:104430. doi:10.1103/PhysRevB.76.104430 CrossRefADSGoogle Scholar
  16. Ohkoshi M, Tamari K, Honda S et al (1984) Perpendicular magnetization in Co–CoO film prepared by reactive rf sputtering. IEEE Trans Magn 20:788–790. doi:10.1109/TMAG.1984.1063381 CrossRefADSGoogle Scholar
  17. Peng DL, Sumiyama K, Hihara T et al (2000) Magnetic properties of monodispersed Co/CoO clusters. Phys Rev B 61:3103–3109. doi:10.1103/PhysRevB.61.3103 CrossRefADSGoogle Scholar
  18. Riveiro JM, De Toro JA, Andrés JP et al (2005) Exchange-bias stabilization of the magnetic nanoparticles in a granular alloy grown by reactive sputtering. Appl Phys Lett 86:172503. doi:10.1063/1.1921353 CrossRefADSGoogle Scholar
  19. Skumryev V, Stoyanov S, Zhang Y et al (2003) Beating the superparamagnetic limit with exchange bias. Nature 423:850–853. doi:10.1038/nature01687 CrossRefPubMedADSGoogle Scholar
  20. Spasova M, Wiedwald U, Farle M et al (2004) Temperature dependence of exchange anisotropy in monodisperse cobalt nanoparticles with a cobalt oxide shell. J Magn Magn Mater 272:1508–1509. doi:10.1016/j.jmmm.2003.12.237 CrossRefADSGoogle Scholar
  21. Tang YJ, Smith DJ, Zink BL et al (2003) Finite size effects on the moment and ordering temperature in antiferromagnetic CoO layers. Phys Rev B 67:054408 and references 5 and 6 thereinCrossRefADSGoogle Scholar
  22. Yamauchi T, Shiiki K (2002) Coercive force of Co–CoO thin films. Jpn J Appl Phys 41:5982–5985. doi:10.1143/JJAP.41.5982 CrossRefADSGoogle Scholar
  23. Yi JY, Platt CL, Rudee ML, Berkowitz AE et al (1996) Sputter deposited Co/CoO composite materials. J Appl Phys 79:5072–5074. doi:10.1063/1.361578 CrossRefADSGoogle Scholar
  24. Yi JB, Ding J, Liu BH et al (2005) Exchange bias and magnetization process of Co/CoO nanocomposite thin films. J Magn Magn Mater 285:224–232. doi:10.1016/j.jmmm.2004.07.044 CrossRefADSGoogle Scholar

Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  • J. A. González
    • 1
  • J. P. Andrés
    • 1
  • J. A. De Toro
    • 1
  • P. Muñiz
    • 1
  • T. Muñoz
    • 1
  • O. Crisan
    • 2
  • C. Binns
    • 2
  • J. M. Riveiro
    • 1
  1. 1.Departamento de Física AplicadaUniversidad de Castilla-La ManchaCiudad RealSpain
  2. 2.Department of Physics and AstronomyUniversity of LeicesterLeicesterUK

Personalised recommendations