Structure and magnetic properties of polycrystalline iron-platium and cobalt-platinum thin films for high density recording media

The goal of this project was to investigate and increase the feasibility of use of FePt and CoPt polycrystalline thin films as high-density recording media, with a focus on targeting perpendicular recording. Understanding the atomic ordering process, developing the proper texture and small grains, lowering the processing temperature and optimizing magnetic properties were the main subjects of this thesis work. In this thesis, nano-structured polycrystalline high anisotropy thin films have been fabricated and characterized. Polycrystalline CoPt and FePt films exhibit perpendicular anisotropy after an annealing process only when their thickness is less than 5 nm. High temperature annealing is still required to obtain an atomically ordered phase with nearly full ordering. The ordering phase transformation is a discontinuous transformation that yields an inhomogeneous microstructure where significant amount of FCC phase remains, unless a long time annealing process is performed.; To lower the atomic ordering temperature, an in-situ ordering process has been performed and the various underlayer structures with an MgO seed layer, have been deposited and investigated. Thin films with thicknesses below 10 nm exhibit perpendicular anisotropy with an average grain size in the range of 10–15 nm in this film. FePt [001] textured films using Pt/Ag seeding layer exhibit lower annealing temperature than FePt/MgO films, while other Ag or Cr seedlayers do not produce faster ordering kinetics. Based on the detailed analysis of nanostructure of FePt thin films, it has been learned that FCC disordered nanoclusters remains in the ordered grains. Detailed observation of magnetic properties and nanostructure by HRTEM suggests that, though a thermally activated component of the switching is observed, the low value of coercivity can be attributed predominantly to reversal processes associated with defect related domain nucleation. We postulate that the nucleation occurs in less ordered regions of the grains. CrMn and Zn overlayer diffusion gives rise to exchange-breaking as determined by magnetic hyteresis observation. Chemical analysis indicated the diffusion of the overlayer material into FePt films, although it was difficult to analyze the composition at the boundaries.