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Co-Ni needle-like and Fe3O4-Pd spherical nanoparticles were prepared by water-in-oil microemulsion (W/O). The as-synthesized nanoparticles have been encapsulated by silica (SiO2) and polyvinyl alcohol (PVA) in N2 atmosphere. Their structure and magnetic properties were evaluated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). The influence of structural modifications to the magnetic properties of nanocomposites has been investigated. Powder X-ray diffraction analysis indicated the formation of face-centered cubic phase for both Co-Ni and Fe3O4-Pd systems. The average crystallite size for the studied samples has been calculated in the range of 7-26 nm. TEM images revealed the morphology of the particles as needle-like nanoparticles for Co-Ni alloy and spherical for Fe3O4-Pd system. The magnetization curves of nanocomposites at room temperature demonstrated coercivity values between 8.2 and 15.5 kA/m for Co-Ni nanocomposites and superparamagnetic behavior of Fe3O4-Pd nanocomposites due to the small-size effect of nanoparticles.
Date of Publication: April 2012