Technical Merit: Data storage is an extremely important component of the information revolution. The dominant branch of the data storage industry is the magnetic hard disk drive. As recording densities increase, so does the approach to the fundamental limit posed by superparamagnetism. Superparamagnetic response refers to the probability of thermally activated switching of magnetic nanoparticle moments with consequent loss of recorded information. The switching frequency becomes larger for a smaller bit size, if not counterbalanced by an increased magnetocrystalline anisotropy energy density of the recording medium. Indeed, the critical (recording medium) limitation in reaching storage densities of 1 Tb/in2 and beyond is that posed by superparamagnetism. As a result, there has been a growing interest in FePt, CoPt and related ferromagnetic alloys with the tetragonal, L10 crystal structure. When deposited at room temperature FePt and CoPt alloy films form the chemically disordered face-centered cubic (fcc or A1) phase. The A1 phase has low magnetocrystalline anisotropy and is consequently unsuitable for use as a recording medium. Post-deposition annealing at high temperatures (> 600 degrees C) or deposition on heated substrates (> 500 degrees C) is necessary to achieve the chemically ordered L10 structure. Such high-temperature processing steps are incompatible with media manufacturing needs and, at present, are major barriers to the implementation of these alloys in recording systems. To move beyond a trial-and-error effort of engineering the alloys for reduced ordering temperature, a deeper fundamental understanding of the A1 to L10 transformation is necessary. Thus, the objective of these studies is to improve understanding of the A1 to L10 transformation in FePt, CoPt and related ternary (FeCuPt, FeNiPt) alloy films, through the measurement of thermodynamic and kinetic parameters of the transformation. A particular emphasis of this research is the effect of alloy chemistry and composition on these parameters. The thermodynamic and kinetic parameters of the transformation (and the Curie temperature of the L10 alloy) in homogeneous binary and ternary alloy films will be measured by differential scanning calorimetry (DSC). The DSC studies of these alloys will be augmented with DSC studies of the formation of the L10 phase in elemental multilayer films of Fe and Pt (Fe/Pt) and Co and Pt (Co/Pt). In addition to DSC, x-ray and electron diffraction studies will be used for phase identification and long-range order parameter measurement, and transmission electron microscopy investigations for characterization of film microstructure. Broader Impact: The program (i) will strongly support undergraduate research in addition to graduate research; (ii) will make an extensive effort to involve students from underrepresented groups; (iii) will support the operation and maintenance of the specialized experimental infrastructure within the PI's laboratories, the Dept. of Materials Science and Eng. and the Data Storage Systems Center (DSSC) at Carnegie Mellon; (iv) will help the development of commercial technology, namely, L10 media for hard disk drives with projected storage capacities of 1 Tb/in2 and beyond. In addition to magnetic recording media, ferromagnetic L10 alloys are being considered for magnetic actuators and other elements in micro/nano-electromechanical systems (MEMS/NEMS). The formation of L10 alloys for these systems similarly involves transformation from a vacuum-deposited A1 phase. Thus, the proposed studies are also expected to be of benefit in the development of these components.
