| The continued demand for faster, smaller, and more efficient power electronic devices can be met in part through the development of materials to meet these demands. Power supplies in computers use a dc-dc converter to deliver various voltages to an increasing assortment of components including processors, disk drives, and displays. At the core of the dc-dc converter is a transformer comprised of a magnetic material which must operate with fewer losses at high frequencies. Current magnetic materials have reached their frequency limit which can be potentially overcome by reducing their dimensions to the nano-scale at which point they become single domain super-paramagnetic particles having no hysteresis loss.;This work explores the synthesis and characteristic properties of ferrite nanoparticles assembled with controlled interparticle spacing into a toroidal monolithic device. Static and high frequency magnetic measurements supported by structural characterization were conducted to determine if nanoparticles can overcome the limitations of their bulk counterparts.;Ten nanometer ferrite particles were synthesized in gram-scale quantities by an aqueous precipitation technique. The ferrite particles exhibited unique structural and magnetic properties including an expanded lattice parameter, compositional variation of the diameter, and a reduced saturation magnetization compared to bulk materials. The surface charge of the particles in solution was found to both stabilize their small size upon formation as well as control their ability to form a good aqueous dispersion. A good dispersion was found to be important in the optimization of a sol-gel process used to coat the ferrite particles with layers of silica ranging from 2 to 15 nm. The silica layer was used to control the distance and magnetic interaction between neighboring nanoparticles as measured by both dc magnetic measurements from room temperature down to 5 K as well as room temperature ac magnetic measurements up to 500 MHz. The results indicate the importance of both individual magnetic nanoparticle structure as well as how they are assembled into a consolidated shape on controlling the magnetic properties of the final material. |
