Thickness reduction in CoPtCr-SiO2 perpendicular recording media to improve media performance

Magnetic properties and recording performance of thin CoPtCr-SiO₂ media were examined in relation to thermal stability. Magnetic anisotropy K_u of {(Co₉₀Cr₁₀)₈₀Pt₂₀}₈₉-(SiO₂)₁₁ media maintains a constant value of around 5.5×10⁶ erg/cm³, even at film thickness of 4 nm. This K_u value corresponds to the anisotropy energy of the grains K_u^g calculated by taking account of the volume fraction of about 8×10⁶ erg/cm³, indicating a high potential to resist thermal agitation. The high K_u derives a high remanence coercivity H_r of ∼4 kOe, even at film thickness of 8 nm, resulting in a loop squareness of nearly 1. The ratio of magnetic anisotropy energy to thermal energy K_uV_act/kT maintained a value of more than 70, even at this thickness. The media noise at low recording density increases with decreasing film thickness below 8 nm, probably due to the thermal agitation. The recording resolution D₅₀ showed a broad maximum of ∼420 kFCI at around this thickness. The reduction in film thickness improves recording resolution; however, it is likely that the large thermal agitation in the thin-film region degrades the recording resolution, resulting in an optimum thickness to show the highest recording resolution.