An analysis of time-dependent magnetization and coercivity and of their relationship to print-through in recording tapes

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Abstract
Time-dependent magnetic phenomena in oxide particulate recording materials are observed by measuring the change of magnetization with time in the presence of a constant field or by measuring the dependence of the hysteresis loop on the field sweep rate. Either type of experiment yields a measured value of the coercivity as a function of the characteristic measurement time. For a constant-field experiment, this time is simply the interval needed for the applied field to reduce the magnetization from saturation remanence to zero. A corresponding time, approximately inverse to the sweep rate, can be associated with the coercivity measured in a swept-field experiment. A time-dependence parameter that measures the strength of the dependence of magnetization on time at constant field and also that of coercivity on sweep rate in a swept-field experiment can be determined. This parameter can be interpreted, using simple kinetic theory, to estimate the volume of the magnetic switching unit. Volumes estimated in this way correlate reasonably well over 2 orders of magnitude with particle volumes determined by electron microscopy. The amount of print-through in recording tapes is found to correlate well with the time-dependence parameter for tapes made from a variety of iron oxide particles both with and without added cobalt.

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