The change with time in the readout signal and the media noise affected by
thermal fluctuation was investigated by micromagnetic computer simulation.
It was found that the logarithm of the time taken for the readout signal to
decay by a constant factor was roughly in proportion to the value of KuV/T
-k regardless of the presence or absence of the distribution in the grain s
ize. The lines representing the logarithm of decay time against KuV/kT were
almost parallel to each other when the decay factor was changed. It was fo
und that the time dependence of the rate of the decay in the readout signal
is similar to that of the rate of the increase in the media noise and that
the change in the media noise preceded the change in the readout signal.