An experimental study of short wavelength recording phenomena

Data is presented which shows that under certain nonbiased sine wave recording conditions the longitudinal magnetization decreases exponentially through the medium thickness. The magnetization is closely described by the expression
M_{x} = M_{x0}e^{KY}/\lambda
where
y
is measured in the negative direction from the medium surface. A demagnetizing field is calculated on the basis of this magnetization profile and a graphical analysis is performed to obtain the quiescent magnetic operating point through the medium. From a knowledge of the magnetization profile with and without self-demagnetization, it is possible to compute the loss in reproduce signal which is attributable to self-demagnetization. Measurements were made of the loss in recorded signal level on media with various magnitudes of saturation magnetization M
s
. The reproduce signal level at long wavelengths is shown to be approximately proportional to M
s
, but at short wavelengths the signal levels converge. If we choose to term the amount of convergence the M
s
-dependent loss, it is shown that the M
s
-dependent loss is much greater than the theoretical self-demagnetization loss. From these results, it can be concluded that other M
s
-dependent losses in addition to self-demagnetization are occurring in the recording process.