Sonochemical synthesis under a magnetic field: fabrication of nickel and cobalt particles and variation of their physical properties.

We report on the variation of the physical properties of nickel and cobalt nanoparticles prepared by using ultrasound irradiation as energy source. First, we describe a sonochemical method for preparing aggregated particles. Second, we interpret the results on the basis of Einstein's theory (1905), which deals with a mathematical expression for the diffusivity of particles into solvents. This theory explains the stability of organosols of nickel and cobalt nanoparticles in polyethylene glycol. Finally, the effect of applying an external magnetic field during sonochemical formation of both aggregated particles and their stable colloids is investigated.