The remanent magnetization in particulate disk coatings

Reliable performance in today´s high areal density digital magnetic recording disk systems requires the optimization of all magnetic and system parameters. The remanent magnetization of the storage surface is one of those important parameters. Major performance limitations are imposed by the writing-demagnetization, and interaction-demagnetization. Minimization of these adverse effects requires a reduction in the thickness of the coating and/or in its remanent magnetization, and a magnetic orientation of the acicular magnetic particles along the circumferential direction of the disk. However, for very high density disk systems such as the IBM 3350 (about 2400 bits/cm and 240 tracks/cm), the reduction in the coating thickness of the disk (down to 0.75-1.0μm) must be compensated by a judicious adjustment of its remanence to ensure adequate output signal. In this study we used the Dynamic Iterative Model to simulate the single pulse, two-pulse, and multiple transition response of an IBM 3350-like channel, and examined the effect of remanence (in the range of 300-1050 Gauss) on resolution, peak shift, and signal output for two values of coating thickness (0.76μm and 1 μm). We conclude that a large remanence is desirable in that it provides a much larger signal while the adverse effect on resolution and peak shift is very small.