High resolution analytical transmission electron microscopy of magnetic recording media

Since the invention of the hard disk drive in 1954, the density of bits per disk has increased exponentially. This trend is partly due to improvements to the magnetic recording media. In current hard disks, each bit is approximately 0.04 mum in its smallest dimension and comprises ∼100 hexagonal close packed Co-alloy magnetic grains. These grains have magnetic "easy" axes oriented longitudinally, or parallel to the film plane. Future recording media have easy axes oriented perpendicular to the film plane. Perpendicular media are expected to provide continued increases in storage density above the limit of longitudinal media.; Quantum-mechanical exchange coupling between magnetic grains degrades the signal-to-noise ratio (SNR) and limits storage density in both media types. Controlling exchange coupling is possible by creating nonmagnetic grain boundaries which compositionally isolate the magnetic grains. High-resolution analytical transmission electron microscopy (TEM) is required to study these media because of their nano-scale grains and grain boundaries. Examining the microstructure and elemental distribution in these films at near atomic level is paramount to understanding their magnetic performance.; The microstructure and elemental distribution in longitudinal and perpendicular media were examined using high resolution analytical TEM techniques, such as energy-filtered TEM (EFTEM), energy-dispersive x-ray spectroscopy (EDS) using a 1.5 nm electron probe, and spectrum imaging with a scanning TEM. These techniques successfully determined how grain boundary Cr segregation varies with grain orientation in longitudinal media. Boundaries misoriented by 0° and 90° commonly occur and were found to have minimal Cr segregation, which limits storage density improvement in these media.; Analytical TEM techniques applied to oxygen-enriched perpendicular media, fabricated using different deposition methods, effectively related microstructure and composition to magnetic properties. The combination of reactive O 2 addition and co-sputtering of TiO2 resulted in O-rich grain boundaries and improved exchange decoupling. A detailed study of TiO 2-enriched perpendicular media found that increasing the volume percent of TiO2 forms more pronounced Ti- and O-rich grain boundaries, decreasing the Co-alloy grain size. Adding more TiO2 creates columnar grains of increasing roughness, yielding composition and thickness variations that test the limitations of the individual analytical techniques and require use of multiple techniques for corroboration.