Optimization of the SiO2 content in CoPtCr-SiO2 perpendicular recording media for high-density recording

Optimization of the SiO₂ content for high-density recording was discussed for {(Co₉₀Cr₁₀)₈₀Pt₂₀}_100-Z-{SiO₂}_Z perpendicular recording media. The grain size D_grain decreases significantly from 8.8 to 5.4 nm as the SiO₂ content Z increases from 0 to 14.4; however, no significant difference in c-axis orientation was observed. Magnetocrystalline anisotropy of grains maintains a large value of nearly 8×10⁶ erg/cm³, even at 10 at % SiO₂ addition, indicating a high potential of perpendicular anisotropy K_u to resist thermal agitation of magnetization. The coercivity H_c increases significantly as the SiO₂ increases, which is coincident with the reduction of the slope of magnetization curve α=4π(dM/dH) due to the enhancement of grain isolation. The H_c shows a maximum at around 11 at % SiO₂ (nearly 30 vol % SiO₂). A further increase of SiO₂ reduces the value of H_c significantly, although the α maintains a constant value of nearly 2, due to thermal agitation of magnetization. The media noise reduces significantly as the SiO₂ increases; however, the addition of SiO₂ beyond about 13 at % leads to a slight increases in media noise probably due to a significant increase of thermal agitation. The recording resolution D₅₀ shows a broad maximum of ∼420 kFCI at around 11 at % SiO₂, suggesting that the D₅₀ is related to the media noise performance. Experimental results indicate that there is a tradeoff to be made between the thermal stability and media noise performance as a function of SiO₂ composition.