Direct observation of magnetization dynamics in spinning magneto-optic discs (invited)

The development of a system capable of direct observation of magnetization and thermal dynamic behavior of magneto-optic recording materials at various relative media-to-laser spot velocities is described along with demonstrations of its value in furthering the understanding of such behavior. A 10-ns-wide observation laser pulse is utilized to produce ‘‘stop-action’’ images of magnetization states in an environment almost identical to that of an actual magneto-optical disc drive operating at linear velocities of 0–40 m/s (7200 rpm, 53 mm radius). Thermal modeling is correlated with images of the instantaneous temperature distributions at various velocities to demonstrate that the thermal conductivity in the materials is approximately 7 W/m/K rather than the bulk 40–50 W/m/K. Techniques for isolating signal due to moving magnetization reversal regions from that due to moving areas of elevated temperature are used to analyze the writing behavior of single layer direct-overwrite recording films.