We have been studying a single-layer Co-Cr perpendicular medium with a thickness of 100-700 nm, using a merged MR head designed for longitudinal recording. The Co78Cr22 medium shows good linearity in its output dependence on the MR bias current. The output is 50% larger than that for a longitudinal medium. A maximum D50 value of 100 kFCI was obtained for a medium with an optimum thickness of 300 nm. The medium noise increases with the medium thickness, whereas the output saturates at 300 nm. The thick medium has two demerits: large write demagnetization and a high level of medium noise. Increasing the Cr content of the Co-Cr medium from 22 to 28 at% significantly reduces these two problems. Cr-rich perpendicular media with thicknesses of over 100 nm are expected to replace longitudinal media in hard disk drives in the near future.
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