On the noise power spectral density of particulate recording media

The ac-noise power spectrum is investigated. Because of the interaction forces between the particles, the structure of the particulate layer has a dominant influence. This structure is quantified by means of the dc-noise power spectrum. Depending on the dispersion and coating technique the duster structure appears to vary. The ac-noise power is described by a mechanism of negative and positive interactions which occur simultaneously. Flux-closuring particles are near to each other at distances less than 0.1 μm, whereas magnetic strings appear to extend over tens of microns.