Erasure in particulate and thin-film disk media

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Abstract
Magnetic recording signals have been written, and subjected to erasure by external magnetic fields, on a variety of longitudinally oriented rigid particulate and thin-film disks. In general, plated thin-film disks are easier to erase than particulate disks, and particulate disks are easier to erase than sputtered thin-film disks. Decaying alternating (ac) erase fields induce greater erasure for a given peak field than do single-direction (dc) erase fields. Successive ac erasures, using the same erase field, induce greater erasure than single ac erasures; while successive dc erasures applied in the same direction do not induce greater erasure than a single dc field erasure. Successive dc erasures where the applied field direction is reversed after each erase application induce additional erasure, but are not as effective as the same number of ac erasures. Erase fields in excess of the disk coercivity induce reductions in signal amplitude, which are attributed to a region of irreversible magnetization switching, and to a region of irreversible approach to saturation as the effects of magnetic inhomogeneities are overcome.

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