Remanence coercivity of recording media in the high speed regime

New measurements of the switching characteristics in short pulse fields of CrO₂ particulate tape and CoNi metal evaporated tape are reported which complete a survey of materials used in flexible media. An unambiguous measure of the results is the remanence coercivity H_CR which increases as pulse width τ decreases. Three mechanisms which could contribute to the increase are thermally assisted switching, damping limited switching and changes in the reversal process. In samples with high viscosity, the results are in excellent agreement over 12 decades with the simple thermal model proposed by Sharrock within the applicable range of τ>1/f₀, where f₀ is the attempt frequency equal to 10⁹ Hz. For τ<1/f₀, H_CR continues to increase; for example, in CrO₂ at τ=0.6 ns, it reaches 1.8 times the value for τ~1.0 s. In samples with low viscosity, the rapid increase in H_CR for τ>1/f₀ in some materials confirms that other mechanisms are dominant in these materials