| Self-assembled monolayer arrays of ferromagnetic nanoparticles (NPs) may enable future magnetic recording with areal densities in the terabits per square inch regime. A transition from conventional granular media to bit patterned media (BPM) presents numerous engineering challenges to which unsatisfactory solutions will result in read and write errors and self-erasing media. To successfully implement monolayer arrays of ferromagnetic NPs as BPM, the following are required: (1) NPs assembled into a regular pattern with circumferential periodicity and equal spacing between bits, (2) uniform magnetic response, which requires uniform volume, shape, composition, crystalline phase, magnetic anisotropy constant and orientation of the crystal axes, (3) minimal interparticle magnetostatic interactions, and (4) thermal stability for extended periods of time (resistance to superparamagnetism).;This dissertation presents a series of studies that address several of the aforementioned engineering challenges. The basis of these studies is the wet-chemical synthesis of ligand-stabilized Ni, Co, and FePt NPs. Two projects examine the synthetic control of Ni(core)/NiO(shell) and Co(core)/CoO(shell) NPs and their magnetic properties. Control of synthetic reactions conditions, specifically ligand type and concentration, dictates NP size. Subsequent magnetic characterization revealed that magnetic properties and exchange bias in particular strongly depend on NP size and oxide shell thickness. In another project, the feasibility of self-assembly of NP monolayers via spin-casting and the implementation of analytical techniques to quantitatively characterize the structure of NP monolayers was investigated. The final two projects involve incorporation of FePt NPs into alumina thin films. The alumina thin film stabilizes monolayers of FePt NPs and facilitates sinter-free phase transformation into FePt intermetallic phases. Transmission electron microscopy characterization reveals that phase transformations from the alloy into intermetallic phases strongly depend on the NP composition.;The application of analytical, structural and magnetic characterization techniques to magnetic NPs elucidated how NP synthetic and self-assembly conditions determine the material structure and properties. These studies provide solutions and insight into overcoming superparamagnetism, controlling the structures of NPs, and fabricating periodic NP assemblies for the application of BPM. |
