Thickness Reduction in CoPtCr–<tex>$hbox SiO_2$</tex>Perpendicular Recording Media to Improve Media Performance

Abstract

Magnetic properties and recording performance of thin CoPtCr-SiO/sub 2/ media were examined in relation to thermal stability. Magnetic anisotropy K/sub u/ of {(Co/sub 90/Cr/sub 10/)/sub 80/Pt/sub 20/}/sub 89/-(SiO/sub 2/)/sub 11/ media maintains a constant value of around 5.5/spl times/10/sup 6/ erg/cm/sup 3/, even at film thickness of 4 nm. This K/sub u/ value corresponds to the anisotropy energy of the grains K/sub u//sup g/ calculated by taking account of the volume fraction of about 8/spl times/10/sup 6/ erg/cm/sup 3/, indicating a high potential to resist thermal agitation. The high K/sub u/ derives a high remanence coercivity H/sub r/ of /spl sim/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/sub u/V/sub 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 D/sub 50/ showed a broad maximum of /spl sim/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.