Our research on magnetic nanoparticles is mainly focused on core/shell structured and ferrite particles. Using either individual or combined techniques that include resistive evaporation and laser ablation in an inert gas condensation system, we synthesize Fe/FeO, Ni/NiO, Co/CoO core/shell, Ni/NiO/CoO multilayered and NiFe2O4 magnetic nanoparticles. These materials are of major interest due to their industrial applications such as ferrofluids, recording tape, flexible recording media as well as biomedical materials. High capacity information storage, for instance, requires smaller particle size that decreasing the particle size lowers the anisotropy energy responsible for holding the magnetic moments along certain directions and it becomes comparable to the thermal energy. This is called as superparamagnetic behavior. Core/shell structured magnetic systems have an extra source of anisotropy that increases the stability of magnetic moments up to certain temperature called blocking temperature. Increasing the blocking temperature as close as possible to room temperature as we keep the particle size small is the main challenge in this field. Although there have been intensive theoretical and experimental research on these materials, lack of a complete theory and variations on the experimental results due to inherit drawbacks of the different synthesis techniques, there is still need for improvement of the existing methods and developing new means to prepare these materials in a controllable manner. By improving the synthesis techniques in our group, we are trying to have a better control on the magnetic properties of nanoparticles. Particles prepared as such let us perform systematic study on their physical properties. Magnetic behaviors of the samples in powder Fe/FeO or composite (Fe/FeO-PMMA) forms are investigated performing various magnetic measurements in a physical property measurement system. Using high resolution microscopy and other structural analysis such as x-ray diffraction and x-ray photoelectron spectroscopy we try to make correlations between the structural and magnetic properties of the nanoparticles.
C. C. Baker, S. K. Hasanain and S. Ismat Shah, "The magnetic behavior of iron oxide passivated iron nanoparticles", J. Appl. Phys.,96, 6657 (2004)
C. C. Baker, S. K. Hasanain and S. Ismat Shah, "Magnetic behavior of iron and iron-oxide nanoparticle/polymer composites", JMMM, 280, 412 (2004)
Abdullah Ceylan, C. C. Baker, S. K. Hasanain and S. Ismat Shah, "Nonmonotonic concentration dependence of magnetic response in Fe nanoparticle-polymer composites", Phys. Rev. B., 72,134411, (2005)
Abdullah Ceylan, C. C. Baker, S. K. Hasanain and S. Ismat Shah, "Effect of Particle Size on the Magnetic Properties of Core-Shell Structured Nanoparticles" J. Appl. Phys. Under review.
Abdullah Ceylan, Abdul. K. Rumaiz and S. Ismat Shah, "Inert Gas Condensation of Evaporated Ni and Laser Ablated CoO", in preparation.