Abstract
Hard disk drives (HDDs) are very important devices for mass data storage, which are widely used in computer systems and cloud storage due to their low cost and high capacity. The development of new materials for recording disks is necessary to further increase the areal density in next-generation magnetic recording media. This dissertation focuses on three main research topics to manipulate the orientation and microstructure of FePt alloys that is a promising candidate as ultrahigh-density perpendicular magnetic recording media. The first topic investigates promotion of the [001]-oriented L10-FePt by rapid thermal annealing (RTA) with a light absorption layer. By using RTA at 400 °C, the highly [001]-oriented L10-FePt grown on SiO2||Si is achieved. Due to the dramatic divergence of the light absorption ability between Si and FePt films, Si behaves as a light absorption layer to absorb much more light emitted from the RTA system, which gives rise to the larger thermal expansion on Si and induces an in-plane tensile stress on FePt films. By raising heating rate during RTA, the transient light intensity is increased; therefore, a higher in-plane tensile stress is exerted on FePt films, which effectively suppresses the opening-up in in-plane hysteresis loops. Furthermore, the (001) texture of the L10-FePt is manipulated by densities of the SiO2 underlayer. The in-plane tensile stress generated during RTA may be released in a loose SiO2 layer, which leads to the worse [001] orientation of the L10-FePt as compared to FePt films on a dense SiO2 layer. The second topic aims at developing L10-FePt nanoparticles (NPs) by thermal dewetting at reduced temperatures. Through in situ heating transmission electron micro-scope (TEM) analysis, the mechanism of the formation process of the L10-FePt NPs is investigated, which demonstrates a typical thermal dewetting process, or called agglom-eration, via holes nucleation and growth. The holes are observed to nucleate and grow along the initial grain boundaries in as-deposited films. Because the evolution of the holes progresses via surface diffusion of atoms, the dewetting process is accelerated at reduced temperatures by adding B2O3 into FePt films due to the low melting point and high diffusivity of B2O3. The accelerated atomic diffusion also enhances the ordering of the L10-FePt. After optimizing thicknesses of the Si light absorption layer, annealing temperatures for the formation of the L10-FePt and FePt NPs can be dramatically decreased from 350 °C to 250 °C and from 700 °C to 500 °C, respectively. The third topic focuses on fabricating periodic FePt NP arrays via templated dewetting of FePt films on a topographic template. Hexagonal-packed SiOC spheres with an average diameter of 25 nm and an average center-to-center distance of 40 nm are obtained on a flat thermally oxidized Si substrate through microphase separation of the PS-PDMS BCP to be used as the topographic templates for templated dewetting. By manipulating thicknesses of FePt films and O2 treatment time of the PS-PDMS BCP, well-ordered FePt NP arrays with a hexagonal packing are fabricated on top of the SiOC spheres. The size of the FePt NPs is around 20 nm that is well confined by the SiOC spheres and the location of these NPs is defined by the SiOC spheres because of their exactly equal center-to-center distances. After treated by Co/NH3 plasma to remove the excess small islands in between the SiOC spheres, a nearly perfect hexagonal-packed FePt nanoparticle array is obtained.