Calculations of external bit fields

The amplitude and distribution of the external fields emanating from recorded transitions are of great interest to technologists in the field of information storage and retrieval and, more particularly, to those studying alternate readout techniques to the conventional inductive readout method. Such areas include the magnetic transfer process, Hall probe techniques, and the magneto-optic and Lorentz beam readout techniques. In this paper we used a harmonic analysis simulation of the non-linear digital recording process, and calculated the amplitude and distribution of external bit fields for a wide range of media magnetic properties and thicknesses, and as a function of bit density and spacing above the surface of the media. Justification for using the harmonic analysis model is based upon the good agreement obtained with the reported spatial behavior of the external bit fields measured directly by a scanning electron microscope. In addition, calculations based on simpler models of a line, step, and linear transition show that the harmonic model is a superior first-order approximation of the nonlinear nature of digital magnetic recording.