Magnetization reversal and activation volume of perpendicular recording media

Magnetization reversal and thermal agitation of magnetization are quantitatively evaluated using a pulse magnetometer for several kinds of perpendicular magnetic recording media. In media with well-segregated grains, magnetization reversal is confirmed to proceed by coherent switching of magnetization, however, intergranular exchange coupling reduces the remanence coercivity, especially in superlattice media and amorphous/granular composite media. The activation volume in CoCr-based alloy media is experimentally indicated to be nearly the same as that of physical grain volume. It is successfully shown that media noise has a clear relation to both activation diameter and the strength of intergranular exchange coupling. It is likely that the values of activation diameter and the strength of intergranular exchange coupling are main factors to determine the cluster size of magnetization, and they must be reduced to improve the media noise performance.