Optimization of the<tex>$hbox SiO_2$</tex>Content in CoPtCr-<tex>$hbox SiO_2$</tex>Perpendicular Recording Media for High-Density Recording

Abstract

Optimization of the SiO/sub 2/ content for high-density recording was discussed for {(Co/sub 90/Cr/sub 10/)/sub 80/Pt/sub 20/}/sub 100-Z/-{SiO/sub 2/}/sub Z/ perpendicular recording media. The grain size D/sub grain/ decreases significantly from 8.8 to 5.4 nm as the SiO/sub 2/ 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/spl times/10/sup 6/ erg/cm/sup 3/, even at 10 at % SiO/sub 2/ addition, indicating a high potential of perpendicular anisotropy K/sub u/ to resist thermal agitation of magnetization. The coercivity H/sub c/ increases significantly as the SiO/sub 2/ increases, which is coincident with the reduction of the slope of magnetization curve /spl alpha/=4/spl pi/(dM/dH) due to the enhancement of grain isolation. The H/sub c/ shows a maximum at around 11 at % SiO/sub 2/ (nearly 30 vol % SiO/sub 2/). A further increase of SiO/sub 2/ reduces the value of H/sub c/ significantly, although the /spl alpha/ maintains a constant value of nearly 2, due to thermal agitation of magnetization. The media noise reduces significantly as the SiO/sub 2/ increases; however, the addition of SiO/sub 2/ beyond about 13 at % leads to a slight increases in media noise probably due to a significant increase of thermal agitation. The recording resolution D/sub 50/ shows a broad maximum of /spl sim/420 kFCI at around 11 at % SiO/sub 2/, suggesting that the D/sub 50/ 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 SiO/sub 2/ composition.