Advanced Magnetic Nanostructures pp 295-324
Media for Extremely High Density Recording
The development and engineering of the magnetic material that stores information largely determines the progress of magnetic storage technology, as epitomized by magnetic hard disks. In this chapter, we consider the ultimate capability for the storage of digital information. Noise performance and spatial resolution are key parameters in recording media and an ongoing challenge in advancing the areal density. The dominant media noise source today is transition jitter noise, or the uncertainty in positioning neighboring bit transitions. In sputtered media, it reflects the finite size, random positioning and dispersions in size, orientation and magnetic properties of the fine grains that comprise the media. Highly anisotropic materials, combined with heat-assisted magnetic recording (HAMR), promise significant reductions in the average, thermally stable grain size from currently about 7–9 nm in Co-alloys to about 2–3 nm in FePt-based media. In addition, self-organized magnetic arrays (SOMA) promise a significant reduction in jitter noise, because they yield nearly monodisperse magnetic nanoparticles such as FePt and Co. SOMA media may serve not only as conventional media with reduced dispersions and media with bit-transitions defined by rows of particles, but may also be scaled to the ultimate goal of single-particle-per-bit recording. In this last scenario, the eventual areal density is governed by the minimal thermally stable size and by the center-to-center spacing of neighboring particles. Ultimately, subject to the mastering of all writability, signal retrieval, bit-addressability and spacing issues, areal densities of the order of 40–50 terabit per square inch may be reached.
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