| Gas phase synthesis processes involve the generation of metal atoms through various means, and the homogeneous nucleation and subsequent condensation and coagulation of nanoparticles. Inert gas condensation (IGC) is a desirable process for the synthesis of metal nanoparticles because it is a relatively simple process capable of producing large quantities of nanoparticles, and since it utilizes vacuum deposition, it offers high purity particles and does not require hazardous chemicals. In this research, the results of the IGC synthesis of iron nanoparticles are presented. The iron nanoparticles are passivated in-situ by slowly introducing oxygen into the chamber to form ferrimagnetic Fe3O4 gamma-Fe2O3 shell/alpha-Fe ferromagnetic core nanoparticles. The magnetic properties of these particles are investigated as a function of passivation layer thickness and particle concentration. The oxide-passivated particles exhibit an exchange bias when cooled below a blocking temperature, which depends on the thickness of the oxide layer present. It was found that the exchange bias increased with oxide thickness. Similarly the blocking temperature also increased with oxide layer thickness. The blocking temperature in all cases, however, was found to be much lower than the Neel temperature for Fe-oxides. The nanoparticles also exhibit a spin glass transition below a characteristic freezing temperature, as evident by a sharp increase in the magnetic moment of the samples. Fe nanoparticle-polymer composite films were also obtained by spin casting mixtures of nanoparticles and polymethylmethacrylate (PMMA). The magnetic properties of these composites were compared to those of particles compressed into pellets. It was observed that when the particles were dispersed into the nanocomposite, the coercivity was increased, suggesting a heightened anisotropy barrier. Similarly, the magnetic relaxation results indicated that the particles dispersed in the PMMA exhibited significantly reduced relaxations through the entire temperature range, as compared to the non-dispersed compressed pellets. It is hoped that this research will result in a greater understanding of the interaction effects between magnetic species. The Fe-oxide/Fe shell/core interactions, may give researchers a better understanding of short-range exchange interactions, while Fe/PMMA composites may elucidate the nature and scope of longer-range dipolar interactions. |
