Noise reduction of magnetic coated disk

We studied the effect of surface roughness on medium noise of a magnetic coated disk, and succeeded in reducing the noise by diminishing this roughness. This low noise disk shows great promise for use at a linear density of as high as 15,000 BPI and a core width of 25 μm. In our studies, we found that the noise was affected mainly by ´as coated´ (i.e. before polishing) roughness and polishing itself did not contribute to noise reduction. Auto-correlation analysis indicated that the ´as coated´ roughness reflected the aggregation of magnetic powder. By improving manufacturing methods of the disk so as to prevent periodic fluctuations in the roughness, we were able to reduce the roughness of the ´as coated´ surface from 0.05 to 0.02 μmRa, and the disk noise 13 to 8 μVrms. Accordingly we obtained an SNR of 41 dB (S = 0.9 mVp-p,N = 8 μVrms) even at a linear density of 15,000 BPI and a core width of 25 μm.