Cluster size and exchange dispersion in perpendicular magnetic media

A computational study of the effects of the intergranular exchange field and its dispersion on the cluster size in perpendicular recording media is presented. The dispersion arises from the grain size dispersion and the dispersion of intrinsic exchange coupling between individual grains. It is found that increasing the degree of dispersion reduces the cluster size due to weakly coupled grains acting as pinning sites against the expansion of the clusters. A simple semi-analytical model is proposed which gives good agreement with the numerical calculations in the limit of the large anisotropy constant.