Fabrication of multilayered superparamagnetic particles based on sequential thermal deposition method

A simple method for the fabrication of superparamagnetic particles was developed. Polystyrene spheres were used as templates, and their surfaces were coated with a magnetic element (Ni) by thermal deposition, controlling their thicknesses strictly. Magnetic properties of fabricated particles depended on the Ni layer thickness; the fabricated particles were typically superparamagnetic for a Ni layer thinner than 3nm and ferromagnetic for a Ni layer thicker than 4nm. For the improvement of the force generated on a particle in a magnetic field, the formation of multiple Ni layers on a particle was examined by sequential depositions of Ni and SiO₂, isolating two Ni layers with a SiO₂ layer. The SiO₂ layer thickness should be larger than 10nm for a sufficient isolation of two Ni layers to maintain the superparamagnetic properties of the particle, and the magnetic charge of the particle increased proportionally with the number of Ni layers on a particle. These results indicate that enhanced superparamagnetic particles with various diameters can easily be fabricated by the suggested method.