MEASUREMENT OF THE SWITCHING SPEED LIMIT IN HIGH COERCIVITY MAGNETIC MEDIA

A microstripline pulse field system has been constructed which allo l7sthe switching speed of high coercivity magnetic media to be measured with pulse widths t greater than or equal to 0.64 ns. The results for gamma Fe2O3 are in good agreement with the previous work in 1974 of Thornley and Williams. A DC bias field H-B was added to the pulse field to allow the high coercivity samples to be switched from saturation to zero remanence and the results ana- lyzed in terms of the switching constant S-w. At H-B = 400 Oe, S-w (Co-gamma Fe2O3)= 158 ns-Oe; at H-B = 700 Oe, S-w (Barium Ferrite) = 135 ns-Oe; at H-B = 720 Oe, S-w (metal particle) = 84 ns-Oe. The value of S-w increased with decreasing bias field particularly for barium ferrite, indicating that in zero bias barium ferrite tapes would be a factor of three slower than metal particle tapes. The pulse width t = t(c) below which time dependent switching was observed was 6 +/- 1, 5 +/- 1, and 1.5 +/- 0.5 ns for Co-gamma Fe2O3, barium ferrite and metal particle samples respectively. These results mean that in a recording system, the media record process should be frequency independent up to at least 250 MHz with metal particle media, but less than 100 MHz with Co-gamma Fe2O3 or barium ferrite media.