Noise reduction and recording density increase in magnetic-coated disks

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Abstract
We studied the effects of several conditions on noise of medium of magnetic‐coated disks and succeeded in reducing the noise significantly. In our study, we focused on nonmagnetic particles and surface roughness and found that: (1) Nonmagnetic particles, like alumina, affect noise unless they are small and as well‐dispersed as the magnetic particles. (2) ’’As‐coated’’ roughness, meaning the surface roughness before polishing, causes the noise. By eliminating nonmagnetic particles and improving the coating method to reduce the ’’as‐coated’’ roughness, we produced extremely low‐noise magnetic‐coated disks. Using Co adsorbed iron oxide powder (Hc:650 Oe), we obtained high signal to noise ratio (SNR) (40 dB) magnetic‐coated disks at a high linear density of 20 000 FRPI.

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