REPTATION AND VISCOSITY IN PARTICULATE RECORDING MEDIA IN THE TIME-LIMITED SWITCHING REGIME

Measurement of P, the percentage reduction in remanence after the application of 1 less-than-or-equal-to n less-than-or-equal-to 10(4) reverse field pulses of width 0.6 ns less-than-or-equal-to tau less-than-or-equal-to 9 ns, are reported for five particulate tape samples including gamma-Fe2O3, Co-gammaFe2O3, Fe, and two different barium ferrites. For tau > tau(c), P depended only on ntau. It increases quite rapidly at small values of ntau depending on the media and then at higher values of ntau approximately linearly with log(nr). In the linear regime, the decrements delta (% change/decade) agree within experimental error with the quasistatic values obtained from viscosity measurements between 10 and 100 s. Considering the arbitrariness of the logarithmic assumption, it is remarkable that the decrement is the same over eleven orders of magnitude. The reduction in P at tau<tau(c) is evidence for time-limited switching as reported previously. However, the dependence of P on ntau for small ntau cannot be explained by the usual viscosity model but is consistent with reptation, a phenomenon suggested by Neel.