Remanence coercivity of recording media in the high speed regime

New measurements of the switching characteristics in short pulse fields of CrO/sub 2/ 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/sub CR/ which increases as pulse width /spl tau/ 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 /spl tau/>1/f/sub 0/, where f/sub 0/ is the attempt frequency equal to 10/sup 9/ Hz. For /spl tau/<1/f/sub 0/, H/sub CR/ continues to increase; for example, in CrO/sub 2/ at /spl tau/=0.6 ns, it reaches 1.8 times the value for /spl tau//spl sim/1.0 s. In samples with low viscosity, the rapid increase in H/sub CR/ for /spl tau/>1/f/sub 0/ in some materials confirms that other mechanisms are dominant in these materials.