Measurements and Analysis of Noise Power Versus Density in Perpendicular Recording

Noise power versus linear density always shows a characteristic non-linearity. At extremely low densities the curve is linear corresponding to the linear sum of transitions. At a medium density the curve becomes nearly flat and then eventually increases to an ac erased state. The loss of the initial linearity occurs at a density where the written transitions over-lap. Above that density the curve is the sum of a decreasing transition noise and an increasing ac erasure noise. A simple model for single grains is presented that gives the entire noise variation: multigrain analysis is left for future studies.