Measurements were made of recording medium noise in erased disks using an in-contact magnetoresistive element and an inductive head supported on an air bearing slider. Four types of coatings on aluminum disks were examined: thin, transition-metal alloy film, CrO2, FeCo particle, and γ-Fe2O3. Results obtained by means of three measurement techniques are in qualitative agreement and indicate that: (1) dc-erased noise of alloy film disks is 14 to 20 dB lower than that of particulate disks measured; (2) dc-erased noise of particulate disks measured is 6 to 16 dB above their bulk-erased noise; (3) although dc noise of particulate disks increases with write current, dc noise of alloy film disks is independent of write current; (4) the shapes of the noise spectra are similar in dc-erased particulate γ-Fe2O3 disks and FeCo particle coated disks; and (5) significant modulation noise is detected on particulate disks but not on alloy film disks. The observed dc-erased noise spectrum is compared with the model for small particle noise and is then used to estimate the size of particle agglomerates or voids.
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IBM Journal of Research and Development
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06 April 2010
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