Time-dependent magnetic phenomena in fine particles used or proposed f
or application in magnetic recording media have been studied by measur
ing the change in magnetization in the presence of a constant field. T
he observed evolution of the magnetization decay, and of the derived p
arameters useful for studying the time effects with the temperature an
d the addition of doping ions, are discussed in relation to the evolut
ion of the magnetic stability and of the magnetization reversal mode.