Transmission electron microscopy studies of longitudinal magnetic recording materials

I describe three studies of materials with potential applications in computer hard drives: the aim of each study was to understand what microstructural features are required for further increases in recording storage density.; In the first study, we used Lorentz Transmission Electron Microscopy (LTEM) to observe the magnetic structure of bits on real hard disks. We wanted to determine how the microstructure affects one's ability to store closely spaced, sharp magnetic-transitions. We used Fresnel-mode-LTEM to observe three disks, which had different hysteresis behaviors and microstructures. We also observed one of the disks using Fresnel-mode-LTEM, Foucault-mode-LTEM, and conventional-mode TEM. In so doing, we were able to observe the magnetic structure of the bits and the physical structure of the magnetic film from the same region of the disk. All of the images from both LTEM modes, however, were of low resolution, which we ascribe to a combination of the moderate M_rt of the disks and the limitations of the microscope. I also discuss the future of LTEM for studying low- M_rt disks.; In the second study, we attempted to deposit Fe₁₆N₂, which has potential in the write head as a core material. We developed a technique to sputter deposit epitaxial (001) Fe-based compounds on(001) Si substrates using a Ag buffer layer. In our efforts, we grew the disordered parent phase to Fe₁₆N₂, α′ nitrogen-martensite, in epitaxial and single phase form. Although we did observe a partial transformation (∼30 volume %) to the ordered Fe₁₆N₂ in α ′ films after post-deposition annealing, we did not observe any Fe₁₆N₂ in the as-deposited films.; In the third study we observed the thin barrier layer in magnetic tunneling junctions (MTJs) using cross-sectional TEM. We studied how AlO_x barriers are formed on Co and PtMnSb. We investigated how position on the substrate, oxidation time, oxygen plasma character, precursor Al thickness, and bottom electrode material affect the final barrier thickness, spread in thickness, and MTJ performance. We show that each of these parameters must be optimized to fabricate high performance MTJs.