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

The magnetic cluster size D_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 H₀ are ∼70% of those calculated using the Stoner-Wohlfarth model taking account of the c-axis distribution, H_r^S-W, even in CoPtCr-SiO₂ media with well segregated grains. Demagnetizing field of magnetic cluster H_d is calculated as a function of the ratio of D_cluster to film thickness, δ. An intrinsic remanence coercivity H₀^int was obtained by compensating the H₀ value by the H_d(H₀^int=H₀+H_d). The H₀^int values are very close to those of H_r^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 H₀.