González, J. A. and Andrés, J. P. and Toro, J. A. and Muñiz, P. and Muñoz, T. and Crisan, O. and Binns, C. and Riveiro, J. M. (2009) Co-CoO nanoparticles prepared by reactive gas-phase aggregation. Journal of Nanoparticle Research, 11 (8). pp. 2105-2111.
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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.
|Uncontrolled Keywords:||Co nanoparticles - Gas-phase aggregation - Exchange-bias - Core-shell particles - Aerosols - Nanocomposites|
|Subjects:||Analytical Science > Microscopy and probe methods|
Physical Science > Nanophysics
Material Science > Nanofabrication processes and tools
|Deposited On:||07 Jan 2010 15:08|
|Last Modified:||07 Jan 2010 15:08|
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