Formation of magnetic cluster and remanence coercivity in granular-type perpendicular media

The magnetic cluster size D/sub cluster/ of perpendicular recording media, which is a main factor in media noise, is discussed in terms of demagnetizing field of magnetic clusters, remanence coercivity, and magnetization switching. It was shown that the values of remanence coercivity obtained by subtracting thermal agitation effect H/sub 0/ are /spl sim/70% of those calculated using the Stoner-Wohlfarth model taking account of the c-axis distribution, H/sub r//sup S-W/, even in CoPtCr-SiO/sub 2/ media with well segregated grains. Demagnetizing field of magnetic cluster H/sub d/ is calculated as a function of the ratio of D/sub cluster/ to film thickness, /spl delta/. An intrinsic remanence coercivity H/sub 0//sup int/ was obtained by compensating the H/sub 0/ value by the H/sub d/(H/sub 0//sup int/=H/sub 0/+H/sub d/). The H/sub 0//sup int/ values are very close to those of H/sub r//sup S-W/, especially in media with well-segregated grains. This result means that the magnetization reversal of these media is mainly determined by coherent rotation of magnetization; however, the demagnetizing field of magnetic cluster, besides thermal agitation effect, reduces the value of H/sub 0/.