DC modulation noise in thin metallic media and its application for head efficiency measurements

A model for one type of modulation noise in thin-film metallic disks is presented based on experimental noise power spectra. It is observed that fluctuations in head-to-disk spacing produce noise proportional to the slope of the hysteresis curve. Experiments on a disk with distinctive surface texture illustrate that spacing variations due to surface texture may indeed be the dominant mechanism in this modulation noise. The data may also be analyzed using a mechanism of coercivity fluctuations. This noise may adversely affect data recording, since it occurs when the magnetization is changing most rapidly. The findings about the noise characteristics give rise to experimental techniques for measuring head efficiency and medium coercivity.