Fabrication and characterization of iron-platinum and cobalt-platinum nanoparticles

The present work was undertaken in order to find materials suitable for ultra-high density recording media that will overcome the thermal stability limitations of current materials.; Nanocomposite CoPt/C and FePt/C thin films have been fabricated in a multilayer form by dc magnetron sputtering from pure CoPt, FePt and C solid targets using a tandem deposition mode and deposited onto naturally oxidized Si (100) substrates. The thicknesses of the magnetic and non-magnetic layers were varied in order to create films with concentrations of carbon. The magnetic properties of these films were studied using a VSM as well as a SQUID magnetometer with applied field up to 55 kOe. The structure and phase transformation was studied using an x-ray diffractometer. The as-made films show a disordered face centered cubic (fcc) structure, which is magnetically soft, and have low coercivity (<20 Oe). The multilayers, were broken and a granular-like structure was obtained by thermal annealing using a conventional vacuum furnace in the temperature range of 500 to 800°C. Magnetic hardening occurs after heat treatment at the higher temperatures, which leads to increase in coercivity to values up to 15 kOe at room temperature. The hardening was due to the formation of nanoparticles with the highly anisotropic; tetragonal. L10 phase (fct) with magnetocrystalline anisotropy K > 107 erg/cm3. Transmission electron microscope studies showed FePt and CoPt particles embedded in C matrix with a size increasing from below 2 nm in the as-made state to a range of 3 to 16 nm in the annealed films. The size distributions were fitted to lognormal curves with relatively narrow width. The interactions between particles were successfully controlled by adjusting the C content in the films and the annealing conditions. These results are very promising and make these materials potential candidates for high-density magnetic recording.